A303220 - OEIS

%I #10 Aug 16 2024 06:07:35

%S 3,7,15,26,57,128,319,849,2285,6395,18072,51914,150497,439554,1292568,

%T 3819778,11341738,33806234,101113152,303345648,912494104,2751564993,

%U 8315282765,25179029388,76381806785,232094778772,706331084162,2152626447195,6569037508556

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

%C First differences of A267574.

%H Chai Wah Wu, <a href="/A303220/b303220.txt">Table of n, a(n) for n = 1..48</a>

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

%e a(1) = 3 because there are 3 1-digit proper prime powers: 2^2 = 4, 2^3 = 8, and 3^2 = 9.

%e 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.

%Y Cf. A267574.

%K nonn,base

%O 1,1

%A _Jon E. Schoenfield_, Apr 19 2018