|
|
A370348
|
|
Numbers k such that there are fewer divisors of prime indices of k than there are prime indices of k.
|
|
19
|
|
|
4, 8, 12, 16, 18, 20, 24, 27, 32, 36, 40, 44, 48, 50, 54, 56, 60, 64, 68, 72, 80, 81, 84, 88, 90, 96, 100, 108, 112, 120, 124, 125, 126, 128, 132, 135, 136, 144, 150, 160, 162, 164, 168, 176, 180, 184, 189, 192, 196, 198, 200, 204, 208, 216, 220, 224, 225, 236, 240, 242, 243, 248, 250, 252, 256
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
No multiple of a term is a term of A368110.
|
|
LINKS
|
|
|
EXAMPLE
|
a(5) = 18 is a term because the prime indices of 18 = 2 * 3^2 are 1,2,2, and there are 3 of these but only 2 divisors of prime indices, namely 1 and 2.
|
|
MAPLE
|
filter:= proc(n) uses numtheory; local F, D, t;
F:= map(t -> [pi(t[1]), t[2]], ifactors(n)[2]);
D:= `union`(seq(divisors(t[1]), t = F));
nops(D) < add(t[2], t = F)
end proc:
select(filter, [$1..300]);
|
|
MATHEMATICA
|
filter[n_] := Module[{F, d},
F = {PrimePi[#[[1]]], #[[2]]}& /@ FactorInteger[n];
d = Union[Flatten[Divisors /@ F[[All, 1]]]];
Length[d] < Total[F[[All, 2]]]];
|
|
CROSSREFS
|
For submultisets instead of parts on the RHS we get A371167.
Partitions of this type are counted by A371171.
A001221 counts distinct prime factors.
A355731 counts choices of a divisor of each prime index, firsts A355732.
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|