A121989 a(n) = (n - 1)*(a(n - 2) - a(n - 3) + 1), a(0) = a(1) = a(2) = 1.

1, 1, 1, 2, 3, 8, 10, 36, 21, 216, -126, 1960, -3751, 25044, -74230, 403144, -1489095, 7638000, -32168046, 164287728, -756314855, 3929115500, -19332654222, 103079467832, -535020703583, 2937890929320, -15952504285350, 90295702455504, -510040670796063, 2974949788743940

Offset

0,4

Links

G. C. Greubel, Table of n, a(n) for n = 0..450 [offset shifted by Georg Fischer, Jun 16 2021]

Formula

a(n) ~ -(-1)^n * c * exp(sqrt(n) - n/2) * n^(n/2 - 1/2), where c = 0.129033591674598655926361807738303723517665374090153324757335... - Vaclav Kotesovec, Jun 16 2021

Mathematica

RecurrenceTable[{a[0]==a[1]==a[2]==1, a[n]==(n-1)a[n-2]-(n-1)a[n-3]+ n-1}, a, {n, 0, 30}] (* Harvey P. Dale, Dec 08 2011 *)

Crossrefs

Sequence in context: A218910 A107401 A165153 * A320843 A010786 A248822

Adjacent sequences: A121986 A121987 A121988 * A121990 A121991 A121992

Keyword

sign,easy

Author

Roger L. Bagula, Sep 11 2006

Extensions

Edited by N. J. A. Sloane, Sep 24 2006

Offset changed to 0 by Georg Fischer, Jun 16 2021

Status

approved