A231756 Numbers n such that reversal (n^2) plus 1 is prime.

1, 2, 5, 8, 9, 10, 15, 16, 17, 20, 26, 29, 46, 50, 51, 52, 79, 80, 81, 83, 90, 92, 94, 100, 142, 144, 149, 150, 159, 160, 161, 162, 167, 168, 170, 171, 172, 173, 200, 246, 247, 251, 254, 255, 258, 259, 260, 262, 264, 283, 284, 287, 289, 290, 297, 299, 449, 454

Offset

1,2

Comments

If n is a multiple of 10, after reversal leading zeros are discarded before adding 1.

Links

K. D. Bajpai, Table of n, a(n) for n = 1..5500

Example

a(3)= 5: 5^2= 25: reversing the digits gives 52: 52+1= 53 which is prime.
a(7)= 15: 15^2= 225: reversing the digits gives 522: 522+1= 523 which is prime.

Maple

with(StringTools):KD:= proc() local a; a:= parse(Reverse(convert((n^2), string)))+1; if isprime(a) then RETURN (n): fi; end: seq(KD(), n=1..1000);

Mathematica

Select[Range[500], PrimeQ[ToExpression[StringReverse[ToString[#^2]]] + 1] &]
Select[Range[500], PrimeQ[IntegerReverse[#^2]+1]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 04 2018 *)

Crossrefs

Cf. A005574 (numbers n: n^2 + 1 is prime).

Cf. A059007 (numbers n: n^2 reversed is a prime).

Sequence in context: A283205 A322916 A062803 * A212591 A153275 A362310

Adjacent sequences: A231753 A231754 A231755 * A231757 A231758 A231759

Keyword

nonn,base

Author

K. D. Bajpai, Nov 21 2013

Status

approved