A167717 Squares that become a prime number when prefixed with a 2.

9, 81, 441, 729, 1089, 1521, 6561, 8649, 16641, 19881, 33489, 53361, 56169, 71289, 74529, 84681, 88209, 103041, 168921, 173889, 251001, 257049, 263169, 269361, 288369, 301401, 314721, 335241, 370881, 423801, 463761, 514089, 549081, 558009

Offset: 1

Author

Claudio Meller, Nov 10 2009

Keywords

• base
• nonn

Comments

Subsequence of squares of A032665. - Michel Marcus, Jun 21 2016

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A032665.

Programs

Mathematica

Select[Range[1, 500, 2]^2, PrimeQ[FromDigits[Join[{2}, IntegerDigits[#]]]] &](* G. C. Greubel, Jun 21 2016 *)
Select[Range[800]^2,PrimeQ[2*10^IntegerLength[#]+#]&] (* Harvey P. Dale, Oct 23 2022 *)