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 A234693 #15 Dec 29 2013 22:26:59 %S A234693 17,101,28901,324901,608401,902501,2016401,5664401,7452901,14822501, %T A234693 16974401,18490001,34222501,40449601,41731601,46240001,48580901, %U A234693 50410001,52417601,76038401,92736901,103022501,111936401,121220101,124768901,139948901,151290001 %N A234693 Primes of the form n^2 + 1 such that (n - 1)^2 + 1 and (n + 1)^2 + 1 are semiprimes. %C A234693 The corresponding n are 4, 10, 170, 570, 780, 950, 1420, 2380... %C A234693 Property: n^2 + 1 = p + q - 1 and for a(n) > 17, a(n) == 1 mod 100. %H A234693 Donovan Johnson and Charles R Greathouse IV, <a href="/A234693/b234693.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Johnson) %e A234693 101 = 10^2 + 1 is in the sequence because 9^2 + 1 = 2*41 and 11^2 + 1 = 2*61. %p A234693 with(numtheory):for n from 1 to 10^5 do:n1:=n^2+1:n2:=(n+1)^2+1:n3:=(n+2)^2+1: if type(n2,prime)=true and bigomega(n1)=2 and bigomega(n3)=2 then printf(`%d, `,n2):else fi:od: %o A234693 (PARI) forstep(n=4,1e5,2,if(isprime(n^2+1) && isprime(n^2/2-n+1) && isprime(n^2/2+n+1), print1(n^2+1", "))) \\ _Charles R Greathouse IV_, Dec 29 2013 %Y A234693 Cf. A002496, A144255, A085722. %K A234693 nonn %O A234693 1,1 %A A234693 _Michel Lagneau_, Dec 29 2013