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 A064067 #7 Aug 03 2017 02:56:57 %S A064067 1,2,3,4,5,5,6,7,6,7,8,9,6,7,8,9,10,7,8,9,10,11,11,8,9,10,11,12,12,13, %T A064067 7,8,9,10,11,11,12,13,8,9,10,11,12,12,13,14,13,9,10,11,12,13,13,14,15, %U A064067 14,15,10,11,12,13,14,14,15,16,15,16,17,7,8,9,10,11,11,12,13,12,13,14 %N A064067 n-th step is to add a(n) to each previous number a(k) (excluding itself, i.e., k < n) to produce n more terms of the sequence, starting with a(0)=1, a(1)=2. %e A064067 Start with (1,2). So after initial step have (1, *2*, 1+2 = 3), then (1, 2, *3*, 1+3 = 4, 2+3 = 5), then (1, 2, 3, *4*, 5, 1+4 = 5, 2+4 = 6, 3+4 = 7), then (1, 2, 3, 4, *5*, 5, 6, 7, 1+5 = 6, 2+5 = 7, 3+5 = 8, 4+5 = 9), etc. %Y A064067 Each positive number appears A063895 number of times. %Y A064067 Cf. A064064, A064065, A064066. %K A064067 nonn %O A064067 0,2 %A A064067 _Henry Bottomley_, Aug 31 2001