This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A303220 #10 Aug 16 2024 06:07:35 %S A303220 3,7,15,26,57,128,319,849,2285,6395,18072,51914,150497,439554,1292568, %T A303220 3819778,11341738,33806234,101113152,303345648,912494104,2751564993, %U A303220 8315282765,25179029388,76381806785,232094778772,706331084162,2152626447195,6569037508556 %N A303220 a(n) is the number of n-digit proper prime powers. %C A303220 First differences of A267574. %H A303220 Chai Wah Wu, <a href="/A303220/b303220.txt">Table of n, a(n) for n = 1..48</a> %F A303220 a(n) = A267574(n) - A267574(n-1). %e A303220 a(1) = 3 because there are 3 1-digit proper prime powers: 2^2 = 4, 2^3 = 8, and 3^2 = 9. %e A303220 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 A303220 Cf. A267574. %K A303220 nonn,base %O A303220 1,1 %A A303220 _Jon E. Schoenfield_, Apr 19 2018