This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A075408 #19 Feb 03 2023 08:18:32 %S A075408 1,4,16,36,100,196,256,400,576,676,1296,1600,2916,3136,4356,5476,7056, %T A075408 8100,8836,12100,13456,14400,15376,15876,16900,17956,21316,22500, %U A075408 24336,25600,28900,30976,32400,33856,41616,42436,44100,50176,52900,55696 %N A075408 Perfect powers pp such that pp+1 is prime. %C A075408 Of 1110 pp's < 10^6, 112 are such that pp+1 is prime and only seven are such that pp-1 is prime (see Mersenne primes (A000668)). %H A075408 Karl-Heinz Hofmann, <a href="/A075408/b075408.txt">Table of n, a(n) for n = 1..10000</a> %F A075408 a(n) = A002496(n) - 1. %e A075408 pp=324900 is OK because pp=570^2 and pp+1=324901 (prime). %t A075408 pp = Join[ Select[ Range[56000], Apply[GCD, Last[ Transpose[ FactorInteger[ # ]]]] > 1 & ]]; Select[pp, PrimeQ[ # + 1] & ] %o A075408 (Python) %o A075408 from sympy import isprime %o A075408 print([n**2 for n in range(1,240) if isprime(n**2 + 1)]) # _Karl-Heinz Hofmann_, Feb 02 2023 %Y A075408 Cf. A001597 (perfect powers), A072868 (pp-1 is prime). %Y A075408 Cf. A002496. %K A075408 easy,nonn %O A075408 1,2 %A A075408 _Zak Seidov_, Oct 11 2002 %E A075408 Edited by _Robert G. Wilson v_, Oct 14 2002 %E A075408 Edited by _N. J. A. Sloane_, Dec 17 2009 at the suggestion of Rick Shepherd