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 A278698 #13 Nov 30 2016 06:37:25
%S A278698 2,3,7,11,13,17,23,53,61,67,73,101,103,107,113,127,251,257,263,311,
%T A278698 317,353,503,523,601,607,613,1303,1567,1753,1877,2503,3023,6257,6263,
%U A278698 6311,6317,6323,6353,6857,6863,7817,8753,9377,12503,12511,12517,12553,12601,12613,12757
%N A278698 Primes p such that every suffix of the base-5 representation of p is either a prime or 1.
%H A278698 Charles R Greathouse IV, <a href="/A278698/b278698.txt">Table of n, a(n) for n = 1..10000</a>
%e A278698 61=221_5 is in the sequence since it is a prime and each of its base-5 suffixes (21_5=11 and 1_5=1) is either prime or 1.
%o A278698 (PARI) expand(v,d)=my(u=List(v), D=5^d); forstep(x=D,4*D,D, for(i=1,#v, if(isprime(t=x+v[i]), listput(u,t)))); Vec(u)
%o A278698 list(lim)=my(v=[1,2,3]); for(n=1,#digits(lim\=1,5)-1, v=expand(v,n)); select(k->k<=lim && k>1, v) \\ _Charles R Greathouse IV_, Nov 26 2016
%o A278698 (PARI) isok(n) = {if (isprime(n), pp = 5^logint(n, 5); while ((isprime(rem=(n % pp)) || (rem == 1)) && (pp != 1), pp = pp/5); pp == 1;);} \\ _Michel Marcus_, Nov 26 2016
%Y A278698 Cf. A143390, A278697.
%K A278698 nonn,base
%O A278698 1,1
%A A278698 _Randy L. Ekl_, Nov 26 2016