OFFSET
1,2
COMMENTS
The first differences never decrease so a very concise sequence from which this sequence can be reconstituted is the number of terms whose first difference is k: 1, 4, 6, 12, 24, 72, 720, 120, 300, 36, 384, 840, 552, 1024, 944, 1680, 840, 2520, ... - Robert G. Wilson v
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..5000
EXAMPLE
MAPLE
with(numtheory): a[1] := 1: for n from 2 to 60 do a[n] := a[n-1] + nops(`intersect`({seq(a[i], i = 1 .. n-1)}, {seq(tau(i), i = 1 .. n-1)})) end do: seq(a[n], n = 1 .. 60); # Emeric Deutsch, Jul 21 2007
MATHEMATICA
f[l_] := Append[l, l[[ -1]] + Count[MemberQ[l, # ] & /@ Union@ DivisorSigma[0, Range@ Length@ l], True]]; Nest[f, {1}, 59] (* Robert G. Wilson v, Aug 26 2007 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Jul 15 2007
EXTENSIONS
More terms from Joshua Zucker and Emeric Deutsch, Jul 18 2007
STATUS
approved