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 A056816 #5 Mar 31 2012 14:45:08 %S A056816 3,5,17,31,193,653,1201,46499,532159,3311233,128199521, %T A056816 20512526282340991,6036724301884645488192191, %U A056816 2170304813579195568101904406358277391153 %N A056816 Primes in the tribonacci sequence A000213. %C A056816 Primes within A000213. %F A056816 a(n) = A000213(A157611(n)). - R. J. Mathar, Dec 14 2011 %Y A056816 Cf. A092836. %K A056816 nonn %O A056816 1,1 %A A056816 _Harvey P. Dale_, Sep 01 2000