OFFSET
1,2
COMMENTS
The records for the number of distinct prime signatures are 1, 2, 3, 4, 6, 8, 9, 12, 16, 18, 20, 24, 32, 36, 40, 48, 60, 64, 72, 80, 96, ... (see the link for more values). - Amiram Eldar, Jul 07 2019
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..60
Amiram Eldar, Table of n, a(n), A182860(a(n)) for n = 1..60
Eric Weisstein's World of Mathematics, Unitary Divisor
EXAMPLE
60 has 8 unitary divisors (1, 3, 4, 5, 12, 15, 20 and 60). Primes 3 and 5 have the same prime signature, as do 12 (2^2*3) and 20 (2^2*5); each of the other four numbers listed is the only unitary divisor of 60 with its particular prime signature. This makes a total of 6 distinct prime signatures that appear among the unitary divisors of 60. Since no positive integer smaller than 60 has more than 4 distinct prime signatures appearing among its unitary divisors, 60 belongs to this sequence.
MATHEMATICA
f[1] = 1; f[n_] := Times @@ (Values[Counts[FactorInteger[n][[;; , 2]]]] + 1); fm = 0; s={}; Do[f1 = f[n]; If[f1 > fm, fm = f1; AppendTo[s, n]], {n, 1, 10^6}]; s (* Amiram Eldar, Jan 19 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Matthew Vandermast, Jan 14 2011
EXTENSIONS
a(14)-a(26) from Amiram Eldar, Jan 19 2019
STATUS
approved