

A117157


a(1)=a(2)=1; a(n) = a(n1)*a(n2) + a(n3) + a(n4) + ... + a(1) for n>2.


1



1, 1, 1, 2, 4, 11, 49, 548, 26872, 14725925, 395715057217, 5827270253948278214, 2305938581960065033611659323852, 13437327306087560724405450621249967248150551970959
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OFFSET

1,4


COMMENTS

Form the product of the previous two terms and then add all other previous terms.


LINKS

Table of n, a(n) for n=1..14.


MATHEMATICA

f[s_] := Block[{}, Append[s, s[[ 1]]s[[ 2]] + Plus @@ Drop[s, 2]]]; Nest[f, {1, 1}, 12] (* Robert G. Wilson v, May 26 2006 *)


PROG

#include <stdio.h> #include <inttypes.h> int main (void) { int64_t n1=1; int64_t n2=1; int i; int64_t sum=0, next; printf("%lld, %lld, ", n1, n2); for (i=0; i<10; i++) { next=n1*n2+sum; sum+=n1; n1=n2; n2=next; printf("%lld, ", n2); } }
(PARI) {m=14; print1(a=1, ", ", b=1, ", "); v=[]; for(n=3, m, print1(k=a*b+sum(j=1, #v, v[j]), ", "); v=concat(v, a); a=b; b=k)} \\ Klaus Brockhaus


CROSSREFS

Cf. A117030.
Sequence in context: A091240 A068488 A096119 * A267013 A318532 A057857
Adjacent sequences: A117154 A117155 A117156 * A117158 A117159 A117160


KEYWORD

nonn


AUTHOR

Gabriel Finch (salsaman(AT)xs4all.nl), Apr 21 2006


EXTENSIONS

a(13) and a(14) from Klaus Brockhaus, Apr 27 2006


STATUS

approved



