1,1

First differences of A267574.

Table of n, a(n) for n=1..29.

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

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.

Cf. A267574.

Sequence in context: A001648 A051054 A001649 * A301894 A213215 A324719

Adjacent sequences: A303217 A303218 A303219 * A303221 A303222 A303223

nonn,base

Jon E. Schoenfield, Apr 19 2018

approved