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

Author

Jon E. Schoenfield, Apr 19 2018

Keywords

• nonn
• base

Comments

First differences of A267574.

Examples

			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.
		

Links

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

Crossrefs

Cf. A267574.

Formula

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