cp's OEIS Frontend

A326149 Numbers whose product of prime indices is divisible by their sum of prime indices.

%I A326149 #13 Jan 11 2021 02:50:11
%S A326149 2,3,5,7,9,11,13,17,19,23,29,30,31,37,41,43,47,49,53,59,61,63,65,67,
%T A326149 71,73,79,81,83,84,89,97,101,103,107,108,109,113,125,127,131,137,139,
%U A326149 149,150,151,154,157,163,165,167,169,173,179,181,190,191,193,197
%N A326149 Numbers whose product of prime indices is divisible by their sum of prime indices.
%C A326149 A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
%C A326149 The Heinz number of an integer partition (y_1,...,y_k) is prime(y_1)*...*prime(y_k), so these are Heinz numbers of integer partitions whose product of parts is divisible by their sum of parts. The enumeration of these partitions by sum is given by A057568.
%H A326149 Amiram Eldar, <a href="/A326149/b326149.txt">Table of n, a(n) for n = 1..10000</a>
%e A326149 The sequence of terms together with their prime indices begins:
%e A326149     2: {1}
%e A326149     3: {2}
%e A326149     5: {3}
%e A326149     7: {4}
%e A326149     9: {2,2}
%e A326149    11: {5}
%e A326149    13: {6}
%e A326149    17: {7}
%e A326149    19: {8}
%e A326149    23: {9}
%e A326149    29: {10}
%e A326149    30: {1,2,3}
%e A326149    31: {11}
%e A326149    37: {12}
%e A326149    41: {13}
%e A326149    43: {14}
%e A326149    47: {15}
%e A326149    49: {4,4}
%e A326149    53: {16}
%e A326149    59: {17}
%t A326149 primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
%t A326149 Select[Range[2,100],Divisible[Times@@primeMS[#],Plus@@primeMS[#]]&]
%Y A326149 Satisfies A056239(a(n))|A003963(a(n)).
%Y A326149 The nonprime case is A326150, with squarefree case A326158.
%Y A326149 Cf. A000720, A001222, A057567, A057568, A112798, A301987.
%Y A326149 Cf. A325037, A325042, A325044, A326151, A326153/A326154, A326155, A326156.
%K A326149 nonn
%O A326149 1,1
%A A326149 _Gus Wiseman_, Jun 09 2019