A353394 Product of prime shadows of prime indices of n (with multiplicity).

1, 1, 2, 1, 2, 2, 3, 1, 4, 2, 2, 2, 4, 3, 4, 1, 2, 4, 5, 2, 6, 2, 3, 2, 4, 4, 8, 3, 4, 4, 2, 1, 4, 2, 6, 4, 6, 5, 8, 2, 2, 6, 4, 2, 8, 3, 4, 2, 9, 4, 4, 4, 7, 8, 4, 3, 10, 4, 2, 4, 6, 2, 12, 1, 8, 4, 2, 2, 6, 6, 6, 4, 4, 6, 8, 5, 6, 8, 4, 2, 16, 2, 2, 6, 4, 4

Offset: 1

Author

Gus Wiseman, May 17 2022

Keywords

• nonn

Comments

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.

We define the prime shadow A181819(n) to be the product of primes indexed by the exponents in the prime factorization of n. For example, 90 = prime(1)*prime(2)^2*prime(3) has prime shadow prime(1)*prime(2)*prime(1) = 12.

Examples

			We have 42 = prime(1)*prime(2)*prime(4), so a(42) = 1*2*3 = 6.
		

Crossrefs

Positions of first appearances are A353397.

A001222 counts prime factors with multiplicity, distinct A001221.

A003963 gives product of prime indices.

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

A124010 gives prime signature, sorted A118914, product A005361.

A181819 gives prime shadow, with an inverse A181821.

A324850 lists numbers divisible by the product of their prime indices.

A325131 lists numbers relatively prime to their prime shadow.

A325755 lists numbers divisible by their prime shadow, quotient also A325756, with recursion A353393.

Cf. A003586, A005117, A008480, A182850, A266477, A289509, A316428, A320325, A325702, A353389, A353395, A353399.

Programs

Mathematica

primeMS[n_]:=If[n==1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];
red[n_]:=If[n==1,1,Times@@Prime/@Last/@FactorInteger[n]];
Table[Times@@red/@primeMS[n],{n,100}]

Formula

a(n) = Product_i A181819(A112798(n,i)).

Positions where a(n) = A003963(n) are A003586.

Positions where a(n) = A005361(n) are A353399, counted by A353398.

Positions where a(n) = A181819(n) are A353395, counted by A353396.