The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A273359 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A273359

Numbers k such that the decimal number concat(4,k) is a square.
(history; published version)

#24 by Michael De Vlieger at Wed Jan 17 09:12:09 EST 2024

STATUS

reviewed

approved

#23 by Amiram Eldar at Wed Jan 17 09:11:11 EST 2024

STATUS

proposed

reviewed

#22 by Michel Marcus at Wed Jan 17 09:08:52 EST 2024

STATUS

editing

proposed

#21 by Michel Marcus at Wed Jan 17 09:08:48 EST 2024

PROG

(PARI) a(n) = {my(k=1, t=0); while(n>k, n-=k; t++; k=floor(sqrt(50)*sqrt(10^t))- ceil(sqrt(41)*sqrt(10^t))+1); (ceil(sqrt(41)*sqrt(10^t))+n-1)^2%(40*10^t)} \\ David A. Corneth, May 20 2016

STATUS

approved

editing

#20 by Charles R Greathouse IV at Thu Sep 08 08:46:16 EDT 2022

PROG

(MAGMAMagma) [n: n in [1..50000 ] | IsSquare(Seqint(Intseq(n) cat Intseq(4)))]; // Vincenzo Librandi, Feb 20 2020

Discussion

Thu Sep 08

08:46

OEIS Server: https://oeis.org/edit/global/2944

#19 by Alois P. Heinz at Thu Feb 20 14:03:35 EST 2020

STATUS

editing

approved

#18 by Alois P. Heinz at Thu Feb 20 14:03:26 EST 2020

NAME

Numbers n k such that the decimal number concat(4, nk) is a square.

EXAMPLE

0 is not a member because 40 is not a square. Note that although 400 is a square, that would require a concatenation with 40 rather than 4.

CROSSREFS

Cf. A272671, A273357, A273358, A273360, A273361, A273362, A273363, A273364.

STATUS

proposed

editing

#17 by Alonso del Arte at Thu Feb 20 13:08:19 EST 2020

STATUS

editing

proposed

#16 by Alonso del Arte at Thu Feb 20 13:06:53 EST 2020

MATHEMATICA

DeleteCases[(FromDigits[Drop[IntegerDigits[#], 1]]) & /@ Select[Range[3, 500]^2, IntegerDigits[#][[1]] == 4 && IntegerDigits[#][[2]] != 0 &], 0] (* Alonso del Arte, Feb 20 2020 *)

Discussion

Thu Feb 20

13:08

Alonso del Arte: That's the fix, just gotta skip 2^2 = 4...

#15 by Alonso del Arte at Thu Feb 20 13:03:14 EST 2020

PROG

(Scala) (5 3 to 500).map(n => n * n).filter(n => n.toString.startsWith("4") && !n.toString.startsWith("40")).map(n => Integer.parseInt(n.toString.substring(1))) // Alonso del Arte, Feb 20 2020

Discussion

Thu Feb 20

13:03

Alonso del Arte: Scastie snippet: (5 to 500).map(n => n * n).filter(n => n.toString.startsWith("4") && !n.toString.startsWith("40")).map(n => Integer.parseInt(n.toString.substring(1)))

13:03

Alonso del Arte: Sorry, I meant to post the URL: https://scastie.scala-lang.org/MlS3T8fDTr68ISHjXXzL0A