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A304521 a(n) is the number of prime powers k such that ceiling(log_2(k)) = n. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Prime powers are defined as numbers of the form p^k with p prime and k >= 1 (A246655).

LINKS

Table of n, a(n) for n=1..37.

EXAMPLE

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.

PROG

(PARI) a(n) = sum(k=2^(n-1)+1, 2^n, isprimepower(k) != 0); \\ Michel Marcus, May 17 2018

CROSSREFS

Cf. A029837, A036378, A246655.

Sequence in context: A006899 A256179 A078830 * A026489 A126312 A126298

Adjacent sequences:  A304518 A304519 A304520 * A304522 A304523 A304524

KEYWORD

nonn

AUTHOR

Jon E. Schoenfield, May 13 2018

STATUS

approved

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Last modified April 6 16:14 EDT 2020. Contains 333276 sequences. (Running on oeis4.)