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 A053178 #19 Jan 21 2021 10:46:27 %S A053178 1,21,51,81,91,111,121,141,161,171,201,221,231,261,291,301,321,341, %T A053178 351,361,371,381,391,411,441,451,471,481,501,511,531,551,561,581,591, %U A053178 611,621,651,671,681,711,721,731,741,771,781,791,801,831,841,851,861,871 %N A053178 Numbers ending in 1 which are not prime. %C A053178 Nonprime numbers of the form k*10+1. - _Juri-Stepan Gerasimov_, Oct 14 2009 %e A053178 a(4) = 91 may look prime to some, but is composite. %p A053178 remove(isprime, [10*j+1$j=0..99])[]; # _Alois P. Heinz_, Jan 21 2021 %o A053178 (PARI) isok(n) = ((n % 10) == 1) && (! isprime(n)) \\ _Michel Marcus_, Jul 26 2013 %o A053178 (Python) %o A053178 from sympy import isprime %o A053178 def aupto(lim): return [m for m in range(1, lim+1, 10) if not isprime(m)] %o A053178 print(aupto(871)) # _Michael S. Branicky_, Jan 21 2021 %Y A053178 Cf. A002808, A017281, A153275. %K A053178 easy,nonn,base %O A053178 1,2 %A A053178 _Enoch Haga_, Feb 29 2000