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 A178553 #9 Mar 15 2020 03:22:43 %S A178553 44449,404449,440441,440443,441443,441449,442447,444043,444047,444341, %T A178553 444343,444347,444349,444401,444403,444421,444461,444463,444469, %U A178553 444473,444487,444547,444641,444649,444841,445447,446441,446447,447443,447449,449441 %N A178553 Primes with exactly four 4's. %H A178553 Daniel Starodubtsev, <a href="/A178553/b178553.txt">Table of n, a(n) for n = 1..10000</a> %o A178553 (PARI) isok(p) = isprime(p) && (#select(x->(x==4), digits(p)) == 4); \\ _Michel Marcus_, Mar 15 2020 %Y A178553 Cf. A038618, A178550, A178551, A178552, A178554, A178555, A178556, A178557, A178558. %K A178553 nonn,base %O A178553 1,1 %A A178553 _Lekraj Beedassy_, May 29 2010 %E A178553 Missing a(13) = 444349 inserted by _Daniel Starodubtsev_, Mar 15 2020