A303220 a(n) is the number of n-digit proper prime powers.

3, 7, 15, 26, 57, 128, 319, 849, 2285, 6395, 18072, 51914, 150497, 439554, 1292568, 3819778, 11341738, 33806234, 101113152, 303345648, 912494104, 2751564993, 8315282765, 25179029388, 76381806785, 232094778772, 706331084162, 2152626447195, 6569037508556

Offset

1,1

Comments

First differences of A267574.

Links

Chai Wah Wu, Table of n, a(n) for n = 1..48

Formula

a(n) = A267574(n) - A267574(n-1).

Example

a(1) = 3 because there are 3 1-digit proper prime powers: 2^2 = 4, 2^3 = 8, and 3^2 = 9.
a(2) = 7 because there are 7 2-digit proper prime powers: 2^4 = 16, 2^5 = 32, 2^6 = 64; 3^3 = 27, 3^4 = 81; 5^2 = 25; and 7^2 = 49.

Crossrefs

Cf. A267574.

Sequence in context: A001648 A051054 A001649 * A301894 A213215 A353578

Adjacent sequences: A303217 A303218 A303219 * A303221 A303222 A303223

Keyword

nonn,base

Author

Jon E. Schoenfield, Apr 19 2018

Status

approved