The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A241013 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A241013

Semiprimes congruent to {1, 2, 4} mod 5.
(history; published version)

#13 by N. J. A. Sloane at Sat Aug 09 23:07:16 EDT 2014

STATUS

proposed

approved

#12 by K. D. Bajpai at Sat Aug 09 23:05:20 EDT 2014

STATUS

editing

proposed

Discussion

Sat Aug 09

23:07

N. J. A. Sloane: I agree with that comment. Primes are interesting. Semiprimes are not. I will approve it, but please try to lift your eyes above semiprimes!

#11 by Alonso del Arte at Thu Aug 07 22:57:58 EDT 2014

MATHEMATICA

Select[Range[1, 500], PrimeOmega[#] == 2 && MemberQ[{1, 2, 4}, Mod[#, 5]] &](* Bajpai *)

Select[Complement[Range[100], 5Range[20] - 2, 5Range[20]], PrimeOmega[#] == 2 &] (* Alonso del Arte, Aug 07 2014 *)

Discussion

Thu Aug 07

23:51

Alonso del Arte: What's interesting about these semiprimes?

#10 by Alonso del Arte at Thu Aug 07 22:51:54 EDT 2014

EXAMPLE

21 = 3 * 7 which is semiprime and Mod[21,5] = 1 mod 5.

39 = 3 * 13 which is semiprime and Mod[39,5] = 4 mod 5.

STATUS

proposed

editing

#9 by Derek Orr at Thu Aug 07 20:20:42 EDT 2014

STATUS

editing

proposed

#8 by Derek Orr at Thu Aug 07 20:20:31 EDT 2014

PROG

(PARI)

for(n=1, 10^4, if(n!=Mod(0, 5)&&n!=Mod(3, 5), if(bigomega(n)==2, print1(n, ", ")))) \\ Derek Orr, Aug 07 2014

KEYWORD

nonn,changed,easy

STATUS

proposed

editing

#7 by K. D. Bajpai at Thu Aug 07 15:15:13 EDT 2014

STATUS

editing

proposed

#6 by K. D. Bajpai at Thu Aug 07 15:14:14 EDT 2014

LINKS

K. D. Bajpai, <a href="/A241013/b241013.txt">Table of n, a(n) for n = 1..11280</a>

#5 by K. D. Bajpai at Thu Aug 07 15:12:13 EDT 2014

NAME

allocated for K. D. Bajpai

Semiprimes congruent to {1, 2, 4} mod 5.

DATA

4, 6, 9, 14, 21, 22, 26, 34, 39, 46, 49, 51, 57, 62, 69, 74, 77, 82, 86, 87, 91, 94, 106, 111, 119, 121, 122, 129, 134, 141, 142, 146, 159, 161, 166, 169, 177, 187, 194, 201, 202, 206, 209, 214, 217, 219, 221, 226, 237, 247, 249, 254, 259, 262, 267, 274, 287, 289

OFFSET

1,1

COMMENTS

Semiprimes in A032793.

EXAMPLE

21 = 3 * 7 which is semiprime and Mod[21,5] = 1.

39 = 3 * 13 which is semiprime and Mod[39,5] = 4.

MATHEMATICA

Select[Range[1, 500], PrimeOmega[#] == 2 && MemberQ[{1, 2, 4}, Mod[#, 5]] &]

CROSSREFS

Cf. A001358, A032793, A045371.

KEYWORD

allocated

nonn,new

AUTHOR

K. D. Bajpai, Aug 07 2014

STATUS

approved

editing

#4 by K. D. Bajpai at Thu Aug 07 15:12:13 EDT 2014

NAME

allocated for K. D. Bajpai

KEYWORD

recycled

allocated