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 A338746 #5 Nov 15 2020 12:55:58 %S A338746 2,1,4,6,8,10,12,3,14,16,18,20,5,22,24,26,9,28,30,11,32,34,15,36,17, %T A338746 38,40,42,19,44,46,48,50,21,23,25,27,52,54,31,33,35,37,56,39,58,60,62, %U A338746 41,64,66,68,70,43,72,74,47,76,78,49,80,82,51,53,55,57,84,86,88,90,92,59,94,96,98,100,102 %N A338746 When a(n) is odd, a(n) is the number of prime digits present so far in the sequence, a(n) included. %e A338746 The first odd term is a(2) = 1 and there is indeed 1 prime digit so far in the sequence (this is the 2 before 1); %e A338746 The next odd term is a(8) = 3 and there are now 3 prime digits so far (2, 2 and 3); %e A338746 The next odd term is a(13) = 5 and there are now 5 prime digits so far (2, 2, 3, 2 and 5); etc. %Y A338746 Cf. A338741, A338742, A338743, A338744, A338745 (variants on the same idea). %K A338746 base,nonn %O A338746 1,1 %A A338746 _Eric Angelini_ and _Carole Dubois_, Nov 07 2020