A068989 Squares which when reversed are primes (ignore leading zeros).

16, 196, 361, 784, 1024, 1369, 1444, 1600, 1681, 3844, 7225, 7921, 9025, 9409, 11236, 14161, 18496, 19321, 19600, 36100, 37249, 38416, 70756, 73441, 75076, 76729, 78400, 78961, 97969, 99856, 102400, 105625, 107584, 109561, 111556, 112225

Offset: 1

Author

Joseph L. Pe, Mar 12 2002

Keywords

• easy
• nonn
• base

Examples

			40^2 = 1600. Reversing the digits we get 0061, which is the prime 61 padded with leading zeroes. Hence 1600 is in the sequence.
41^2 = 1681. Reversing the digits we get 1861, which is a prime. Hence 1681 is in the sequence.
42^2 = 1764. Reversing the digits we get 4671 = 3^3 * 173. So 1764 is not in the sequence.
		

Links

• T. D. Noe, Table of n, a(n) for n=1..1000

Crossrefs

Cf. primes whose reversal is a square, A007488; numbers n such that n^2 reversed is a prime, A059007.

Programs

Mathematica

Do[s = i^2; If[PrimeQ[FromDigits[Reverse[IntegerDigits[s]]]], Print[s]], {i, 1, 10^2}] (* Pe *)
Select[Range[100]^2, PrimeQ[FromDigits[Reverse[IntegerDigits[#]]]] &] (* Alonso del Arte, Jan 07 2018 *)

PARI

isok(n) = issquare(n) && isprime(fromdigits(Vecrev(digits(n)))); \\ Michel Marcus, Jan 07 2018

Extensions

More terms from Zak Seidov, Jan 26 2005

Edited by N. J. A. Sloane, Dec 23 2007