A079854 a(1) = 1, a(k) divides a(k+r) for all k and r and the ratios a(k+r)/a(k) are all different.

1, 1, 2, 6, 24, 120, 840, 6720, 60480, 604800, 6652800, 86486400, 1210809600, 18162144000, 308756448000, 4940103168000, 88921857024000, 1689515283456000, 35479820952576000, 780556060956672000, 17952789402003456000

Offset

1,3

Links

Table of n, a(n) for n=1..21.

Example

a(7) != 120*1, 120*2, ..., 120*6 as the ratios 1,2,3,...,6 appeared as 1/1, 2/1, 6/2, 24/6, 120/24, 6/1. So a(7) = 7*120 = 840.

Mathematica

f[l_List] := Block[{n = Length[l], w, k = 1, r = l[[ -1]]/l}, w = Flatten[Table[Take[l, i - n]/l[[i]], {i, n}]]; While[Intersection[w, k*r] != {}, k++ ]; Append[l, k*l[[ -1]]]]; Nest[f, {1}, 21] (* Ray Chandler, Feb 08 2007 *)

Crossrefs

Cf. A000045, A066720, A079852, A036241.

Sequence in context: A292749 A351984 A365977 * A024923 A334395 A347064

Adjacent sequences: A079851 A079852 A079853 * A079855 A079856 A079857

Keyword

nonn

Author

Amarnath Murthy, Feb 19 2003

Extensions

Corrected and extended by Fung Cheok Yin (cheokyin_restart(AT)yahoo.com.hk), Sep 30 2006

Edited and further extended by Ray Chandler, Feb 08 2007

Status

approved