login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A333051 a(1) = 1; a(n+1) = Sum_{d|n, gcd(d, n/d) = 1} a(n/d) * a(d). 2
1, 1, 2, 4, 8, 16, 36, 72, 144, 288, 592, 1184, 2384, 4768, 9608, 19248, 38496, 76992, 154272, 308544, 617152, 1234448, 2470080, 4940160, 9880608, 19761216, 39527200, 79054400, 158109088, 316218176, 632456976, 1264913952, 2529827904, 5059658176, 10119393344, 20238787264 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
MAPLE
a[1]:= 1:
for n from 1 to 40 do
P:= ifactors(n)[2];
k:= nops(P);
t:= 0;
for S in combinat:-powerset(k) do
d:= mul(P[i][1]^P[i][2], i=S);
t:= t + a[d]*a[n/d]
od;
a[n+1]:= t
od:
seq(a[i], i=1..41); # Robert Israel, Mar 09 2020
MATHEMATICA
a[1] = 1; a[n_] := a[n] = Sum[If[GCD[(n - 1)/d, d] == 1, a[(n - 1)/d] a[d], 0], {d, Divisors[n - 1]}]; Table[a[n], {n, 1, 36}]
CROSSREFS
Sequence in context: A195327 A266544 A348414 * A034340 A034341 A341536
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Mar 06 2020
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 14 05:31 EDT 2024. Contains 371655 sequences. (Running on oeis4.)