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A184999
Smallest number having exactly n partitions into distinct parts, with each part divisible by the next.
3
0, 3, 6, 9, 12, 15, 22, 25, 21, 30, 48, 36, 40, 56, 51, 45, 57, 64, 84, 76, 63, 90, 85, 93, 81, 99, 100, 91, 150, 130, 105, 133, 126, 147, 154, 184, 135, 153, 198, 213, 175, 304, 165, 265, 232, 183, 320, 171, 226, 210, 201, 274, 300, 243
OFFSET
1,2
LINKS
FORMULA
a(n) = min { k : A122651(k) = n }.
EXAMPLE
a(7) = 22, because A122651(22) = 7 and A122651(m) <> 7 for all m<22. The 7 partitions of 22 into distinct parts, with each part divisible by the next are: [22], [21,1], [20,2], [18,3,1], [16,4,2], [14,7,1], [12,6,3,1].
MAPLE
with(numtheory):
a:= proc() local t, a, b, bb;
t:= -1;
a:= proc() -1 end;
bb:= proc(n) option remember;
`if`(n=0, 1, add(bb((n-d)/d), d=divisors(n) minus{1}))
end:
b:= n-> `if`(n=0, 1, bb(n)+bb(n-1));
proc(n) local h;
while a(n) = -1 do
t:= t+1;
h:= b(t);
if a(h) = -1 then a(h):= t fi
od; a(n)
end
end():
seq(a(n), n=1..100);
MATHEMATICA
b[0]=1; b[n_] := b[n] = Sum[b[(n-d)/d], {d, Divisors[n] // Rest}]; a[0] = 1; a[n_] := For[k=0, True, k++, If[b[k]+b[k-1] == n, Return[k]]]; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Dec 03 2014, after Alois P. Heinz *)
CROSSREFS
Sequence in context: A123581 A187337 A371000 * A289761 A310151 A310152
KEYWORD
nonn,look
AUTHOR
Alois P. Heinz, Mar 28 2011
STATUS
approved