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A304521
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a(n) is the number of prime powers k such that ceiling(log_2(k)) = n.
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1
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1, 2, 3, 4, 8, 9, 17, 26, 47, 81, 142, 264, 474, 883, 1629, 3045, 5735, 10780, 20429, 38688, 73654, 140426, 268341, 513867, 986034, 1894410, 3646135, 7027826, 13562626, 26208249, 50698866, 98184468, 190338062, 369326691, 717271794, 1394198587, 2712112562
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OFFSET
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1,2
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COMMENTS
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Prime powers are defined as numbers of the form p^k with p prime and k >= 1 (A246655).
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LINKS
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EXAMPLE
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a(1)=1 because the interval [2,2] contains 1 prime power: 2.
a(2)=2 because the interval [3,4] contains 2 prime powers: 3 and 4=2^2.
a(3)=3 because the prime powers in [5,8] are 5, 7, and 8=2^3.
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PROG
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(PARI) a(n) = sum(k=2^(n-1)+1, 2^n, isprimepower(k) != 0); \\ Michel Marcus, May 17 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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