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 A072688 #6 Oct 21 2024 04:39:24 %S A072688 1,2,3,3,3,4,5,6,6,7,7,7,7,7,8,9,9,9,9,9,9,9,10,10,10,10,11,12,12,12, %T A072688 12,12,13,13,13,13,14,15,15,16,16,16,16,16,16,16,16,16,16,17,17,17,17, %U A072688 17,17,17,17,17,17,18,18,18,18,18,18,18,18,18,18,19,19 %N A072688 Of the first n integers (inclusive), how many of them have a prime number of letters in their English names? %F A072688 a(n)=number of terms of A072685 <= n. %e A072688 Sequence A072685 begins: 1, 2, 3, 6, 7, 8, 10 so there are 3 terms up to and including n=4, 3 terms up to and including n=5, 6 terms up to and including n=9. Therefore a(4)=3, a(5)=3, a(9)=6. %Y A072688 Cf. A072685, A072687. %K A072688 easy,nonn,word %O A072688 1,2 %A A072688 Mark Hudson (mrmarkhudson(AT)hotmail.com), Jul 02 2002 %E A072688 a(17) onward corrected by _Sean A. Irvine_, Oct 20 2024