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 A186689 #12 Mar 10 2015 01:42:08 %S A186689 3,5,7,8,10,11,12,13,14,17,18,21,22,23,26,29,30,32,35,36,38,39,40,42, %T A186689 50,52,57,58,61,62,65,68,71,72,73,78,81,84,86,92,94,98,100,102,103, %U A186689 105,108,112,113,114,115,116,119,120,122,124,128,129,130,138,146,148,152,153,158 %N A186689 Numbers n such that n^4 + 1 is a semiprime. %C A186689 Corresponding semiprimes n^4+1 are in A186688. %H A186689 Robert Price, <a href="/A186689/b186689.txt">Table of n, a(n) for n = 1..1500</a> %e A186689 3 is in the sequence because 3^4 + 1 = 82 = 2*41 is semiprime. %t A186689 SemiPrimeQ[ n_] := (n > 1) && (2 == Plus @@ (Transpose[FactorInteger[n]][[2]])); %t A186689 Select[Range[300], SemiPrimeQ[#^4 + 1] &] %t A186689 Select[Range[200],PrimeOmega[#^4+1]==2&] (* _Harvey P. Dale_, Jan 27 2013 *) %Y A186689 Cf. A001358, A006313, A085722, A103854, A104238, A104335, A105041, A105066, A105078, A105122, A105142, A105237, A104479, A104494, A104657, A105282, A186688. %K A186689 nonn %O A186689 1,1 %A A186689 _Michel Lagneau_, Feb 25 2011