A111465 a(1) = 1, a(n+1) = a(n)/T(n+1), if T(n+1) divides a(n), else a(n+1) = a(n) *T(n+1), where T(n) = n*(n+1)/2 is a triangular number (A000217).

1, 3, 18, 180, 12, 252, 9, 324, 14580, 801900, 12150, 947700, 86240700, 821340, 98560800, 13404268800, 87609600, 14981241600, 78848640, 16558214400, 3824947526400, 967711724179200, 3506201899200, 11687339664, 3798385390800

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Maple

T:=n->n*(n+1)/2: a[1]:=1: for n from 1 to 28 do if type(a[n]/T(n+1), integer)=true then a[n+1]:=a[n]/T(n+1) else a[n+1]:=a[n]*T(n+1) fi od: seq(a[n], n=1..29); # Emeric Deutsch, Aug 11 2005

Mathematica

nxt[{n_, a_}]:=Module[{tr=((n+1)(n+2))/2}, {n+1, If[Divisible[ a, tr], a/tr, a*tr]}]; Transpose[NestList[nxt, {1, 1}, 30]][[2]] (* Harvey P. Dale, Aug 22 2014 *)

Crossrefs

Cf. A000217.

Sequence in context: A080687 A231619 A223895 * A247029 A108994 A006472

Adjacent sequences: A111462 A111463 A111464 * A111466 A111467 A111468

Keyword

easy,nonn

Author

Amarnath Murthy, Aug 05 2005

Extensions

More terms from Emeric Deutsch, Aug 11 2005

Status

approved