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A231756 Numbers n such that reversal (n^2) plus 1 is prime. 2
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 (list; graph; refs; listen; history; text; internal format)
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 A161154

Adjacent sequences:  A231753 A231754 A231755 * A231757 A231758 A231759

KEYWORD

nonn,base

AUTHOR

K. D. Bajpai, Nov 21 2013

STATUS

approved

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Last modified September 21 05:55 EDT 2020. Contains 337267 sequences. (Running on oeis4.)