

A122961


Alternately form product and sum of all previous terms.


2



1, 1, 1, 3, 3, 9, 81, 99, 649539, 649737, 274124633198656977, 274124633199956451, 20598907656583661830059012023854018733151994905840579, 20598907656583661830059012023854019281401261305753481
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,4


COMMENTS

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.


LINKS

Iain Fox, Table of n, a(n) for n = 1..18
Iain Fox, Table of n, a(n) for n = 1..34


FORMULA

a(1) = a(2) = 1. For n > 1, a(2n1) = a(2n3)^2 * a(2n2), a(2n) = 2 * a(2n2) + a(2n1).


PROG

(PARI) first(n) = my(res = vector(n, i, 1)); for(x=4, n, res[x]=if(x%2, prod(i=1, x1, res[i]), sum(i=1, x1, res[i]))); res \\ Iain Fox, Oct 29 2018
(PARI) first(n) = my(res = vector(n, i, 1)); for(x=4, n, res[x]=if(x%2, res[x1]*res[x2]^2, res[x1]+2*res[x2])); res \\ Iain Fox, Oct 29 2018


CROSSREFS

Cf. A039941, A000004, A320603.
Sequence in context: A334774 A257627 A115564 * A165421 A227432 A100731
Adjacent sequences: A122958 A122959 A122960 * A122962 A122963 A122964


KEYWORD

nonn


AUTHOR

Franklin T. AdamsWatters, Oct 26 2006


STATUS

approved



