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%I #14 May 22 2018 04:27:27
%S 1,2,3,4,8,9,17,26,47,81,142,264,474,883,1629,3045,5735,10780,20429,
%T 38688,73654,140426,268341,513867,986034,1894410,3646135,7027826,
%U 13562626,26208249,50698866,98184468,190338062,369326691,717271794,1394198587,2712112562
%N a(n) is the number of prime powers k such that ceiling(log_2(k)) = n.
%C Prime powers are defined as numbers of the form p^k with p prime and k >= 1 (A246655).
%e a(1)=1 because the interval [2,2] contains 1 prime power: 2.
%e a(2)=2 because the interval [3,4] contains 2 prime powers: 3 and 4=2^2.
%e a(3)=3 because the prime powers in [5,8] are 5, 7, and 8=2^3.
%o (PARI) a(n) = sum(k=2^(n-1)+1, 2^n, isprimepower(k) != 0); \\ _Michel Marcus_, May 17 2018
%Y Cf. A029837, A036378, A246655.
%K nonn
%O 1,2
%A _Jon E. Schoenfield_, May 13 2018
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