A249589 Numbers whose square with initial (= leftmost) digit removed is a prime.

5, 17, 19, 21, 23, 27, 29, 31, 33, 39, 49, 51, 53, 69, 71, 77, 79, 87, 91, 97, 143, 147, 151, 157, 159, 163, 171, 173, 187, 191, 199, 201, 229, 231, 233, 239, 241, 243, 247, 251, 267, 279, 283, 293, 297, 301, 321, 333, 351, 357, 363, 369, 381, 393, 423, 447, 449, 453, 457, 463, 467, 469, 471, 477, 483, 491, 493, 501, 511, 517, 523

Offset

1,1

Comments

The squares are in A225873.

Links

Harvey P. Dale and Davin Park, Table of n, a(n) for n = 1..20000 [Terms 1 through 1000 were computed by Harvey P. Dale and terms 1001 through 20000 by Davin Park]

Mathematica

Select[Range[600], PrimeQ[FromDigits[Rest[IntegerDigits[#^2]]]]&] (* Harvey P. Dale, Dec 13 2015 *)
b /. Flatten[Outer[Solve[a + #2*10^#1 == b^2 && 0 <= a < 10^#1 && Sqrt[#2*10^#1] <= b < Sqrt[10^(#1 + 1)] && a \[Element] Primes, {a, b}, Integers] &, Range[0, 5], Range[9]], 2] (* Davin Park, Dec 30 2016 *)

Prog

(PARI) is=(n)->isprime(n^2%10^(#Str(n^2)-1))

Crossrefs

Cf. A227916, A225873.

Sequence in context: A275629 A351974 A364935 * A040153 A038896 A117382

Adjacent sequences: A249586 A249587 A249588 * A249590 A249591 A249592

Keyword

nonn,base

Author

M. F. Hasler, Nov 01 2014

Extensions

Extended by Davin Park, Dec 30 2016

Status

approved