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 A033640 #10 Apr 14 2021 12:04:02 %S A033640 1,1,2,1,3,7,6,20,52,6,26,104,32,162,460,356,1438,4048,712,3588,15272, %T A033640 5012,27460,90476,64944,300816,912472,90476,155420,611656,1067892, %U A033640 1770024,4763360,4151704,14746316,39566064,8915064,27813084,109938548,76294212,222960908 %N A033640 Base 3 digital convolution sequence. %H A033640 Alois P. Heinz, <a href="/A033640/b033640.txt">Table of n, a(n) for n = 0..2000</a> %e A033640 Suppose base = 3 and a(0)..a(13) are 1 1 2 1 3 7 6 20 52 6 26 104 32 162. In base 3, 14 = 112, so we convolve the last three terms with 1, 1, 2 to obtain 104*1+32*1+162*2 = 460. %p A033640 a:= proc(n) option remember; `if`(n=0, 1, (l-> %p A033640 add(l[i]*a(n-i), i=1..nops(l)))(convert(n, base, 3))) %p A033640 end: %p A033640 seq(a(n), n=0..40); # _Alois P. Heinz_, Apr 14 2021 %Y A033640 Cf. A033639, A033641, A033642, A033643, A033644, A033645, A033646, A033647. %K A033640 base,nonn %O A033640 0,3 %A A033640 _David W. Wilson_