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 A263876 #19 Dec 01 2019 07:16:05 %S A263876 7,18,38,41,68,70,182,239,500,682,776,800,1068,1710,1744,4030,4060, %T A263876 5604,5744,8119,12156,15006,16610,17684,21490,25294,26884,27590,32060, %U A263876 32150,37416,37520,45630,47321,58724,71264,84906,88526,98864,109054,109610,128766 %N A263876 Numbers n such that n^2 + 1 has two distinct prime divisors less than n. %C A263876 Subsequence of A256011. %C A263876 The numbers n such that n^2 + 1 = p*q are semiprimes (A085722) are not in the sequence. According to this property, the corresponding sequence of the number of prime divisors with multiplicity is 3, 3, 3, 3, 4, 3, 5, 5, 3, 5, 3, 3, 7, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 6, ... %H A263876 Amiram Eldar, <a href="/A263876/b263876.txt">Table of n, a(n) for n = 1..500</a> %e A263876 7 is in the sequence because 7^2 + 1 = 2*5^2 => 2 and 5 are less than 7. %t A263876 Select[Range[150000], PrimeNu[#^2+1] == 2&&FactorInteger[#^2+1][[1,1]]<# &&FactorInteger[#^2+1][[2,1]]<#&] %o A263876 (PARI) for(n=1, 1e5, t=n^2+1; if ((omega(t) == 2) && (factor(t)[, 1][2] < n), print1(n, ", "))); \\ _Altug Alkan_, Oct 28 2015 %Y A263876 Cf. A085722, A144255, A256011, A263877. %K A263876 nonn %O A263876 1,1 %A A263876 _Michel Lagneau_, Oct 28 2015