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 A381239 #4 Mar 16 2025 18:24:17
%S A381239 2,3,7,13,19,31,37,41,43,47,53,59,71,83,89,97,101,103,107,109,113,127,
%T A381239 131,137,139,149,151,157,163,181,191,193,197,199,211,227,233,239,251,
%U A381239 257,263,269,271,277,281,283,293,307,313,331,337,347,349,353,359
%N A381239 Primes of the form Sum_{k >= 0} floor(m/5^k) for some number m.
%e A381239 floor(16/1) + floor(16/5) = 19, so 19 is in the sequence.
%t A381239 f[n_] := Sum[Floor[n/5^k], {k, 0, Floor[Log[5, n]]}] (* A191610 *)
%t A381239 u=Select[Range[400], PrimeQ[f[#]] &]
%t A381239 Map[f, u]
%Y A381239 Cf. A191610, A380662.
%K A381239 nonn
%O A381239 1,1
%A A381239 _Clark Kimberling_, Mar 09 2025