OFFSET
1,2
LINKS
FORMULA
a(n) = 1+A324923(n). - Antti Karttunen, Oct 23 2023
EXAMPLE
20 is the Matula-Goebel number of the tree (oo((o))), which has 4 distinct terminal subtrees: {(oo((o))), ((o)), (o), o}. So a(20) = 4.
See also illustrations in A061773.
MATHEMATICA
ids[n_]:=Union@@FixedPointList[Union@@(Cases[If[#==1, {}, FactorInteger[#]], {p_, _}:>PrimePi[p]]&/@#)&, {n}];
Table[Length[ids[n]], {n, 100}]
PROG
(PARI)
A006530(n) = if(1==n, n, my(f=factor(n)); f[#f~, 1]);
A324923(n) = { my(lista = List([]), gpf, i); while(n > 1, gpf=A006530(n); i = primepi(gpf); n /= gpf; n *= i; listput(lista, i)); #Set(lista); }; \\ Antti Karttunen, Oct 23 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 05 2018
EXTENSIONS
Data section extended up to a(108) by Antti Karttunen, Oct 23 2023
STATUS
approved