A245283 a(n) = a(n-1) * (a(n-1) + a(n-2)) / a(n-4) with a(1) = a(2) = a(3) = a(4) = 1.

1, 1, 1, 1, 2, 6, 48, 2592, 3421440, 1952520007680, 79423772100432548659200, 2433694280407609647520301298079459442688000, 1731103819002733625504286414686785477293241305893841298989509923950758461440000

Offset

1,5

Links

G. C. Greubel, Table of n, a(n) for n = 1..17

Formula

a(n+3) = a(n+2) * A245384(n) for n>0.

Mathematica

a[ n_] := If[ n<5, 1, a[n] = a[n-1] (a[n-1] + a[n-2]) / a[n-4]];
RecurrenceTable[{a[n] == a[n-1]*(a[n-1] + a[n-2])/a[n-4], a[1] == a[2] == a[3] == a[4] == 1}, a, {n, 1, 10}] (* G. C. Greubel, Aug 06 2018 *)
nxt[{a_, b_, c_, d_}]:={b, c, d, d (d+c)/a}; NestList[nxt, {1, 1, 1, 1}, 15][[All, 1]] (* Harvey P. Dale, Jun 25 2021 *)

Prog

(PARI) {a(n) = if( n<5, 1, a(n-1) * (a(n-1) + a(n-2)) / a(n-4))};
(Magma) I:=[1, 1, 1, 1]; [n le 4 select I[n] else Self(n-1)*(Self(n-1) + Self(n-2))/Self(n-4): n in [1..10]]; // G. C. Greubel, Aug 06 2018

Crossrefs

Cf. A245384.

Sequence in context: A096313 A346788 A230053 * A126023 A088679 A161766

Adjacent sequences: A245280 A245281 A245282 * A245284 A245285 A245286

Keyword

nonn

Author

Michael Somos, Aug 21 2014

Status

approved