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 A139901 #24 Jul 14 2019 17:11:50 %S A139901 31,79,151,199,271,439,631,751,919,991,1039,1231,1279,1399,1471,1759, %T A139901 1831,1879,1951,1999,2239,2311,2551,2671,2719,2791,3079,3271,3319, %U A139901 3391,3511,3559,3631,3919,4111,4159,4231,4519,4591,4639,4759,4831 %N A139901 Duplicate of A139855. %K A139901 dead %O A139901 1,1