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A121812 a(n) = a(n-4)*a(n-3) + a(n-4)*a(n-2) + a(n-3)*a(n-2) + a(n-4)*a(n-1) + a(n-3)*a(n-1) + a(n-2)*a(n-1). 1
0, 1, 1, 1, 3, 12, 67, 1123, 93127, 112028175, 10566272277846, 1184716081561127371921, 12518165521628430511804483358652025, 14830472137388987962469618424964700332186681194373079941 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,5
LINKS
FORMULA
a(n) = sum_{j=2..4} sum_{1<=k<j} a(n-j)*a(n-k). [Oct 14 2009]
MATHEMATICA
a[0] = 0; a[1] = 1; a[2] = 1; a[3] = 1; a[n_] : a[n] = a[ -4 + n] a[ -3 + n] + a[ -4 + n] a[ -2 + n] + a[ -3 + n] a[ -2 + n] + a[ -4 + n] a[ -1 + n] + a[ -3 + n] a[ -1 + n] + a[ -2 + n] a[ -1 + n] b = Table[a[n], {n, 0, 15}]
nxt[{a_, b_, c_, d_}]:={b, c, d, Total[Times@@@Subsets[{a, b, c, d}, {2}]]}; NestList[nxt, {0, 1, 1, 1}, 20][[;; , 1]] (* Harvey P. Dale, Sep 26 2023 *)
CROSSREFS
Sequence in context: A107103 A107887 A187118 * A039750 A365655 A366228
KEYWORD
nonn
AUTHOR
Roger L. Bagula, Aug 30 2006
EXTENSIONS
Definition replaced by recurrence - The Assoc. Editors of the OEIS, Oct 14 2009
STATUS
approved

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Last modified February 24 01:16 EST 2024. Contains 370288 sequences. (Running on oeis4.)