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 A065684 #16 Dec 15 2024 11:01:23
%S A065684 0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
%T A065684 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
%U A065684 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,4,5,6,7,8,9,10,11
%N A065684 Number of primes <= prime(n) which begin with a 5.
%H A065684 Harry J. Smith, <a href="/A065684/b065684.txt">Table of n, a(n) for n = 1..1000</a>
%e A065684 a(i) = 1 for 2 < i < 16 and a(16) = 2 as 53 = A000040(16) is the second prime beginning with 5. a(664579) = 72951 (A000040(664579) = 9999991 is the largest prime < 10^7).
%t A065684 Accumulate@ Array[Boole[First@ IntegerDigits@ Prime@ # == 5] &, 103] (* _Michael De Vlieger_, Jun 14 2018 *)
%o A065684 (PARI) lista(n) = { my(a=[p\10^logint(p,10)==5 | p<-primes(n)]); for(i=2, #a, a[i]+=a[i-1]); a} \\ _Harry J. Smith_, Oct 26 2009
%Y A065684 Cf. A000040, A045711, A065680.
%K A065684 base,nonn
%O A065684 1,16
%A A065684 _Reinhard Zumkeller_, Nov 13 2001