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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, 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
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
KEYWORD
nonn
AUTHOR
Leroy Quet, Jul 08 2008
EXTENSIONS
Extended beyond a(20) by R. J. Mathar, Aug 08 2008
STATUS
approved