A076041 a(n) = n! for n < 4; else a(n) = floor(P(n-1)/n) where P(n) = a(1) * a(2) * ... * a(n).

1, 2, 6, 3, 7, 42, 1512, 2000376, 3556892570112, 11386336279786153952123289, 117862412614885811248635740101130996768076206774085

Offset

1,2

Comments

Original definition: a(1)=1, a(n)=n*P(n-1) if P(n-1) < n, a(n) = floor(P(n-1)/n) if n <= P(n-1), where P(n-1) = a(1) * a(2) * ... * a(n-1).

Next term a(12) = 1273391928...9197035520 ~ 1.27*10^100 has 101 digits. - M. F. Hasler, Oct 21 2014

Links

Table of n, a(n) for n=1..11.

Example

a(4) = floor(1*2*6/4) = 3.
a(5) = floor(1*2*6*3/5) = floor(36/5) = 7.

Mathematica

a[1] = 1; p[n_] := Product[a[k], {k, 1, n}]; a[n_ /; p[n-1] < n] := a[n] = n*p[n-1]; a[n_ /; n < p[n-1]] := a[n] = Floor[p[n-1]/n]; Table[a[n], {n, 1, 12}] (* Jean-François Alcover, Jul 22 2013 *)

Prog

(PARI) a(n)=if(n<4, n!, P=3!; for(i=3, n-1, P*=P\i); P\n) \\ M. F. Hasler, Oct 21 2014

Crossrefs

Cf. A076039, A003462, A076042, A046901.

Sequence in context: A154129 A176014 A011447 * A156816 A021383 A296456

Adjacent sequences: A076038 A076039 A076040 * A076042 A076043 A076044

Keyword

nice,nonn,easy

Author

Amarnath Murthy, Oct 29 2002

Extensions

Corrected and extended by Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 20 2003

Edited by M. F. Hasler, Oct 21 2014

Status

approved