A232655 Primes p such that reversal (p^2+p) is also prime.
5, 13, 19, 103, 139, 181, 193, 271, 277, 313, 379, 433, 577, 619, 631, 853, 859, 883, 1093, 1117, 1123, 1237, 1279, 1321, 1741, 1873, 1933, 1987, 2659, 2707, 2713, 2719, 2767, 2791, 3163, 3217, 3271, 3331, 3469, 3529, 3547, 3631, 3637, 3727, 3907, 3943, 4129, 4177
Offset: 1
Examples
a(2)= 13, it is prime: n= 6, prime(6)= 13: reversal(13^2+13)= 281, which is also prime. a(4)= 103, it is prime: n= 27, prime(27)= 103: reversal(103^2+103)= 21701, which is also prime. a(6)= 181, it is prime: n= 42, prime(42)= 181: reversal(181^2+181)= 24923, which is also prime.
Links
- K. D. Bajpai, Table of n, a(n) for n = 1..6650
Crossrefs
Programs
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Maple
with(StringTools): KD:= proc() local a, p; p:=ithprime(n); a:= parse(Reverse(convert((p^2+p), string))); if isprime(a) then RETURN (p): fi; end: seq(KD(), n=1..3000);
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Mathematica
Select[Prime[Range[3000]], PrimeQ[FromDigits[Reverse[IntegerDigits[#^2 + #]]]] &]