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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
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 8 08:56 EST 2021. Contains 349594 sequences. (Running on oeis4.)