This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A117030 a(1) = a(2) = 1; a(n) = a(n-1)*a(n-2) - a(n-3) - a(n-4) - ... - a(1) for n>2. 1

%I

%S 1,1,1,0,-2,-3,3,-10,-28,279,-7803,-2177000,16987130758,

%T -36980983660158439,-628200804994572838287982201,

%U 23231483704802676028750227275477328286998042,-14594036764575342428539025427350979161630036659925283421091485142638200

%N a(1) = a(2) = 1; a(n) = a(n-1)*a(n-2) - a(n-3) - a(n-4) - ... - a(1) for n>2.

%C Form the product of the previous two terms and then subtract all other previous terms.

%C Additionally, with a(1)=1, a(2)=2, this gives: 1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10... cf. A008619.

%t f[s_] := Block[{}, Append[s, s[[ -1]]s[[ -2]] - Plus @@ Drop[s, -2]]]; Nest[f, {1, 1}, 15] (* _Robert G. Wilson v_, May 26 2006 *)

%o (C) #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<12;i++) { next=n1*n2-sum; sum+=n1; n1=n2; n2=next; printf("%lld,",n2); } }

%o (PARI) {m=16;a=1;b=1;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_

%Y Cf. A008619, A117157.

%K sign

%O 1,5

%A Gabriel Finch (salsaman(AT)xs4all.nl), Apr 16 2006

%E a(12) corrected; a(15) and a(16) from _Klaus Brockhaus_, Apr 17 2006

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 15 17:03 EST 2019. Contains 330000 sequences. (Running on oeis4.)