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 A138218 #17 May 26 2024 18:59:20 %S A138218 1,3,6,7,14,17,18,22,24,25,27,28,29,31,32,41,46,48,50,52,55,59,62,64, %T A138218 66,67,76,77,83,85,87,88,92,94,95,97,102,106,108,118,123,134,136,139, %U A138218 140,141,147,148,154,155,157,162,165,167,179,181,192,193,199,202,203,207 %N A138218 Numbers k such that 180k^2 + 1 is prime. %C A138218 Or, numbers j arising in A137530. %H A138218 Harvey P. Dale, <a href="/A138218/b138218.txt">Table of n, a(n) for n = 1..1000</a> %F A138218 a(n) = sqrt((A137530(n) - 1)/180). %t A138218 Select[Range[250],PrimeQ[180#^2+1]&] (* _Harvey P. Dale_, May 26 2024 *) %o A138218 (Magma) [n: n in [0..10000]|IsPrime(1+180*n^2)] // _Vincenzo Librandi_, Dec 13 2010 %o A138218 (PARI) is(n)=isprime(1+180*n^2) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A138218 Cf. A137530. %K A138218 nonn,easy %O A138218 1,2 %A A138218 _Zak Seidov_, May 05 2008