OFFSET
0,7
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000
EXAMPLE
a(10) = #{10, 8+1+1, 6+1+1+1+1, 10x1} = 4;
a(11) = #{10+1, 8+1+1+1, 6+1+1+1+1+1, 11x1} = 4;
a(12) = #{10+1+1, 8+1+1+1+1, 6+6, 6+6x1, 12x1} = 5;
a(13) = #{10+1+1+1, 8+1+1+1+1+1, 6+6+1, 6+7x1, 13x1} = 5;
a(14) = #{14, 10+1+1+1+1, 8+6, 8+6x1, 6+6+1+1, 6+8x1, 14x1} = 7;
a(15) = #{15, 14+1, 10+1+1+1+1+1, 8+6+1, 8+7x1, 6+6+1+1+1, 6+9x1, 15x1} = 8;
a(16) = #{15+1, 14+1+1, 10+6, 10+6x1, 8+8, 8+6+1+1, 8+8x1, 6+6+1+1+1+1, 6+10x1, 16x1} = 10.
MAPLE
with(numtheory):
a:= proc(n) option remember; `if`(n=0, 1, add(a(n-j)*(add(
`if`(tau(d)=4, d, 0), d=divisors(j))+1), j=1..n)/n)
end:
seq(a(n), n=0..100); # Alois P. Heinz, Mar 23 2017
MATHEMATICA
a[n_] := a[n] = If[n == 0, 1, Sum[a[n-j]*(Sum[If[DivisorSigma[0, d] == 4, d, 0], {d, Divisors[j]}] + 1), {j, 1, n}]/n];
Table[a[n], {n, 0, 100}] (* Jean-François Alcover, Apr 12 2017, after Alois P. Heinz *)
PROG
(Haskell)
a236473 = p a007422_list where
p _ 0 = 1
p ks'@(k:ks) m = if m < k then 0 else p ks' (m - k) + p ks m
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 26 2014
STATUS
approved