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 A122961 #8 Oct 30 2018 09:43:45 %S A122961 1,1,1,3,3,9,81,99,649539,649737,274124633198656977, %T A122961 274124633199956451, %U A122961 20598907656583661830059012023854018733151994905840579,20598907656583661830059012023854019281401261305753481 %N A122961 Alternately form product and sum of all previous terms. %C A122961 Note that definition does not make a(1) a special case; it is the empty product, which is 1. If we started with addition, the sequence would be all zeros. %H A122961 Iain Fox, <a href="/A122961/b122961.txt">Table of n, a(n) for n = 1..18</a> %H A122961 Iain Fox, <a href="/A122961/a122961.txt">Table of n, a(n) for n = 1..34</a> %F A122961 a(1) = a(2) = 1. For n > 1, a(2n-1) = a(2n-3)^2 * a(2n-2), a(2n) = 2 * a(2n-2) + a(2n-1). %o A122961 (PARI) first(n) = my(res = vector(n, i, 1)); for(x=4, n, res[x]=if(x%2, prod(i=1, x-1, res[i]), sum(i=1, x-1, res[i]))); res \\ _Iain Fox_, Oct 29 2018 %o A122961 (PARI) first(n) = my(res = vector(n, i, 1)); for(x=4, n, res[x]=if(x%2, res[x-1]*res[x-2]^2, res[x-1]+2*res[x-2])); res \\ _Iain Fox_, Oct 29 2018 %Y A122961 Cf. A039941, A000004, A320603. %K A122961 nonn %O A122961 1,4 %A A122961 _Franklin T. Adams-Watters_, Oct 26 2006