A265147 a(1) = 2, a(n) = smallest number > a(n-1) such that the concatenation of a(n-1) and a(n) is a square.

2, 5, 29, 241, 1809, 6516, 27729, 70281, 191236, 537636, 5052601, 24352064, 50491721, 335176900, 816286736, 1584582656, 5835352241, 31064957504, 299026078001, 368254999225, 916181280225, 6283970794161, 31966212255489, 247575988078441, 558234718638336, 4773574731628096

Offset

1,1

Links

Table of n, a(n) for n=1..26.

Example

a(3) is 29 since it is the least number greater than a(2)=5 which concatenated with 5 forms a perfect square, i.e., 529 = 23^2.

Mathematica

f[n_] := Block[{x = n, d = 1 + Floor@ Log10@ n}, q = (Floor@ Sqrt[(10^d + 1) x] + 1)^2; If[q < (10^d) (x + 1), Mod[q, 10^d], Mod[(Floor@ Sqrt[(10^d)(10x + 1) - 1] + 1)^2, 10^(d + 1)] ]]; NestList[f, 2, 25] (* after the algorithm of David W. Wilson in A090566 *)

Crossrefs

Cf. A090566, A265148, A265149, A265150, A265151, A265152, A265153, A265154, A265155.

Sequence in context: A277005 A350922 A007014 * A098682 A108367 A191621

Adjacent sequences: A265144 A265145 A265146 * A265148 A265149 A265150

Keyword

nonn,base

Author

Robert G. Wilson v, Dec 02 2015

Status

approved