A140644 a(0)=1. a(n) = a(n-1)/d(n) if d(n) divides a(n-1). Otherwise, a(n) = a(n-1)*d(n). (d(n) is the number of positive divisors of n.).

1, 1, 2, 1, 3, 6, 24, 12, 3, 1, 4, 2, 12, 6, 24, 6, 30, 15, 90, 45, 270, 1080, 270, 135, 1080, 360, 90, 360, 60, 30, 240, 120, 20, 5, 20, 5, 45, 90, 360, 90, 720, 360, 45, 90, 15, 90, 360, 180, 18, 6, 1, 4, 24, 12, 96, 24, 3, 12, 3, 6, 72, 36, 9, 54, 378, 1512, 189, 378, 63

Offset

0,3

Links

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Maple

A140644 := proc(n) option remember ; local d ; if n = 0 then 1; else d := numtheory[tau](n) ; if A140644(n-1) mod d = 0 then RETURN( A140644(n-1)/d ) ; else RETURN( d*A140644(n-1) ) ; fi; fi; end: for n from 0 to 80 do printf("%d, ", A140644(n)) ; od: # R. J. Mathar, Aug 08 2008

Mathematica

nxt[{n_, a_}]:=Module[{d=DivisorSigma[0, n+1]}, {n+1, If[Divisible[a, d], a/d, a*d]}]; Transpose[NestList[nxt, {0, 1}, 70]][[2]] (* Harvey P. Dale, Jul 25 2015 *)

Crossrefs

Cf. A008336.

Sequence in context: A024741 A024961 A260666 * A321651 A326308 A073901

Adjacent sequences: A140641 A140642 A140643 * A140645 A140646 A140647

Keyword

nonn

Author

Leroy Quet, Jul 08 2008

Extensions

Extended beyond a(20) by R. J. Mathar, Aug 08 2008

Status

approved