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Revision History for A347530 (Bold, blue-underlined text is an addition; faded, red-underlined text is a deletion.)

Showing entries 1-10 | older changes
Primes of the form (p^2 + 9)/2 where p is prime.
(history; published version)
#17 by Sean A. Irvine at Sun Oct 10 15:19:51 EDT 2021
STATUS

proposed

approved

#16 by Jon E. Schoenfield at Sun Sep 05 17:20:00 EDT 2021
STATUS

editing

proposed

Discussion
Sun Sep 05
17:23
Jon E. Schoenfield: I already did. :-)
17:23
Burak Muslu: Thanks :)
17:24
Jon E. Schoenfield: Given that, for all primes p > 5, p^2 exceeds a multiple of 120 by either 1 or 49, it's not too hard to show that all terms here other than a(n) == 29 (mod 60) for all terms other than a(1).
17:25
Jon E. Schoenfield: Um ... let me try that again.  :-/
17:25
Jon E. Schoenfield: Given that, for all primes p > 5, p^2 exceeds a multiple of 120 by either 1 or 49, it's not too hard to show that a(n) == 29 (mod 60) for all terms other than a(1).
17:31
Burak Muslu: i missed your help Mr. Schoenfield. Shall I add the last part you wrote to the continuation of the comment section that you made the correction?
17:53
Jon E. Schoenfield: I thought maybe you'd like to prove that a(n) = 29 (mod 60), and then -- if you wanted to -- add another line to the Comments section stating and proving that result. :-)  But if you'd rather not, that's fine.  I just noticed that all the listed terms other than 17 had 9 as their last digit, and wondered why that was, and then found the result about a(n) mod 60.
Mon Sep 06
00:11
Burak Muslu: Thanks Mr. Schoenfield. I understand. In the following sequence((p^2+25)/2 ), the last digits are 3 and 7, maybe I'll add a general sentence about all of them later. I didn't add all the sequences at the same time, because it might not be suitable for Oeis. However, in parallel with your explanation, I will consider a general statement.
#15 by Jon E. Schoenfield at Sun Sep 05 17:19:47 EDT 2021
COMMENTS

Each p is an odd number, so p^2 == 1 (mod 8), thus (p^2 + 9)/2 == 1 (mod 14).

STATUS

proposed

editing

Discussion
Sun Sep 05
17:20
Jon E. Schoenfield: I meant like this. :-)
17:22
Burak Muslu: Hi Mr. Schoenfield. Thank you also for your help in the comment section. It's ok for me. If you want, I can press the ready button again.
#14 by Jon E. Schoenfield at Sun Sep 05 17:18:48 EDT 2021
STATUS

editing

proposed

#13 by Jon E. Schoenfield at Sun Sep 05 17:18:29 EDT 2021
COMMENTS

Half the sum of the squares of two prime numbers, one of which is 3.

Each p is also xan odd number, so p^2 == 1 (mod 8), thus (p^2 + 9)/2, if x is prime, as expected x == 1 (mod4mod 1).

is also if we consider the form as (p^2+3^2)/2 all the elements of the form are also prime numbers.

STATUS

proposed

editing

Discussion
Sun Sep 05
17:18
Jon E. Schoenfield: Does this look okay?
#12 by David A. Corneth at Sun Sep 05 16:51:09 EDT 2021
STATUS

editing

proposed

Discussion
Sun Sep 05
16:58
Burak Muslu: Let the comments section be as you, the editors, see fit. If I remember correctly, Fermat had a theorem that the sum of two squares equals 1(mod4).
17:11
David A. Corneth: Odd squares are 1 (mod 4) as they are squares of odd numbers. Odd numbers are of the form 2k + 1 and so they are squared (2k + 1)^2 = 4*k^2 + 4k + 1 = 4(k^2 + k) + 1 == 1 (mod 4). For (p^2 + 3)/2 to be an integer, p needs to be odd. As p^2 == 1 (mod 4), p^2 + 9 == 2 (mod 4) and so (p^2 + 9)/2 == 1 (mod 4).
17:18
Burak Muslu: Thanks for your helps. If I delete the other two sentences in the comment section and add the proof you wrote to the continuation of the second sentence, is it appropriate for you?
#11 by David A. Corneth at Sun Sep 05 16:44:17 EDT 2021
CROSSREFS

Subsequence of A076727 and of A103739.

STATUS

proposed

editing

Discussion
Sun Sep 05
16:50
David A. Corneth: I'd only state terms are 1 (mod 4) with proof, if any. The rest is clear from the name or numerology I think.
#10 by David A. Corneth at Sun Sep 05 16:41:35 EDT 2021
STATUS

editing

proposed

#9 by David A. Corneth at Sun Sep 05 16:41:24 EDT 2021
EXAMPLE

17 is in the sequence as 17 = (5p^2 + 9)/2 where p = 17,5 is prime.

29 is in the sequence as 29 = (7p^2 + 9)/2 where p = 29 and so on7 is prime.

STATUS

proposed

editing

#8 by Amiram Eldar at Sun Sep 05 16:32:32 EDT 2021
STATUS

editing

proposed

Discussion
Sun Sep 05
16:38
David A. Corneth: Do we need 3 versions of the name with just small rewordings as comments?
16:39
David A. Corneth: this seems quite tedious to do manually, not to speak of the risk of errors.
16:43
Burak Muslu: I may have used unnecessary and excessive sentences in the comment section. Honestly, I need your help on that part Mr. Corneth. I can use wolfram. either I couldn't do it or the program didn't find it. Then i tried manually. Sorry for mistakes.