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 A381973 #14 Aug 05 2025 00:12:03
%S A381973 2,4,9,12,14,17,22,28,36,41,42,46,49,61,66,69,71,73,86,89,94,101,102,
%T A381973 107,110,113,121,129,131,134,143,151,153,155,158,169,173,177,181,187,
%U A381973 190,211,214,223,227,235,238,250,254,257,274,281,282,289,295,301
%N A381973 Numbers m such that Sum_{k >= 0} floor(m/3^k) is prime.
%C A381973 Includes 3^(k-1) for k in A028491. - _Robert Israel_, Apr 21 2025
%H A381973 Robert Israel, <a href="/A381973/b381973.txt">Table of n, a(n) for n = 1..10000</a>
%e A381973 [9/1] + [9/3] + [9/9] = 13, where [ ] = floor, so 9 is in the sequence.
%p A381973 f:= proc(n) add(floor(n/3^k),k=0..ilog[3](n)) end proc:
%p A381973 select(m -> isprime(f(n)), [$2..1000]); # _Robert Israel_, Apr 21 2025
%t A381973 f[n_] := Sum[Floor[n/3^k], {k, 0, Floor[Log[3, n]]}] (* A004128 *)
%t A381973 u = Select[Range[400], PrimeQ[f[#]] &] (* A381973 *)
%t A381973 Map[f, u] (* A381974 *)
%Y A381973 Cf. A000040, A028491, A381974.
%K A381973 nonn
%O A381973 1,1
%A A381973 _Clark Kimberling_, Apr 01 2025