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Product of multiplicities of the prime exponents (signature) of n; a(1) = 0.
15

%I #15 Oct 20 2024 16:39:11

%S 0,1,1,1,1,2,1,1,1,2,1,1,1,2,2,1,1,1,1,1,2,2,1,1,1,2,1,1,1,3,1,1,2,2,

%T 2,2,1,2,2,1,1,3,1,1,1,2,1,1,1,1,2,1,1,1,2,1,2,2,1,2,1,2,1,1,2,3,1,1,

%U 2,3,1,1,1,2,1,1,2,3,1,1,1,2,1,2,2,2,2

%N Product of multiplicities of the prime exponents (signature) of n; a(1) = 0.

%C Warning: If the prime multiplicities of n are a multiset y, this sequence gives the product of multiplicities in y, not the product of y.

%C Differs from A351946 at A351946(1260) = 4, a(1260) = 2.

%C Differs from A327500 at A327500(450) = 3, a(450) = 2.

%C We set a(1) = 0 so that the positions of first appearances are the primorials A002110.

%C Also the product of the prime metasignature of n (row n of A238747).

%H Robert Israel, <a href="/A353507/b353507.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A005361(A181819(n)) = A003963(A181819(A181819(n))).

%e The prime signature of 13860 is (2,2,1,1,1), with multiplicities (2,3), so a(13860) = 6.

%p f:= proc(n) local M,s;

%p M:= ifactors(n)[2][..,2];

%p mul(numboccur(s,M),s=convert(M,set));

%p end proc:

%p f(1):= 0:

%p map(f, [$1..100]); # _Robert Israel_, May 19 2023

%t Table[If[n==1,0,Times@@Length/@Split[Sort[Last/@FactorInteger[n]]]],{n,100}]

%t Join[{0},Table[Times@@(Length/@Split[FactorInteger[n][[;;,2]]]),{n,2,100}]] (* _Harvey P. Dale_, Oct 20 2024 *)

%o (Python)

%o from math import prod

%o from itertools import groupby

%o from sympy import factorint

%o def A353507(n): return 0 if n == 1 else prod(len(list(g)) for k, g in groupby(factorint(n).values())) # _Chai Wah Wu_, May 20 2022

%Y Positions of first appearances are A002110.

%Y The prime indices themselves have product A003963, counted by A339095.

%Y The prime signature itself has product A005361, counted by A266477.

%Y A001222 counts prime factors with multiplicity, distinct A001221.

%Y A056239 adds up prime indices, row sums of A112798 and A296150.

%Y A071625 counts distinct prime exponents (third omega).

%Y A124010 gives prime signature, sorted A118914.

%Y A130091 lists numbers with distinct prime exponents, counted by A098859.

%Y A181819 gives prime shadow, with an inverse A181821.

%Y A238747 gives prime metasignature, sorted A353742.

%Y A323022 gives fourth omega.

%Y Cf. A085629, A097318, A182850, A304678, A353394, A353399, A353500, A353503.

%K nonn

%O 1,6

%A _Gus Wiseman_, May 19 2022