A304194 - OEIS

A304194

Numbers k such that k = Product (p_j^e_j) = Product (pi(p_j)*p_j), where pi() = A000720.

1, 2, 12, 56, 180, 304, 336, 936, 1696, 1824, 2484, 5040, 5328, 6664, 8384, 8512, 9900, 10176, 13176, 14040, 25632, 26208, 27360, 33372, 33712, 37260, 39808, 39984, 47488, 50304, 51072, 52200, 65232, 69552, 79920, 126900, 128448, 142272, 149184, 152640, 162648, 167776, 184064, 193752, 197640

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OFFSET

1,2

COMMENTS

Numbers k such that A007947(k)*A156061(k) = k or A156061(k) = A003557(k).

LINKS

Table of n, a(n) for n=1..45.

Eric Weisstein's World of Mathematics, Distinct Prime Factors

Index entries for sequences computed from indices in prime factorization

EXAMPLE

9900 is a term because 9900 = 2^2 * 3^2 * 5^2 * 11 = prime(1)^2 * prime(2)^2 * prime(3)^2 * prime(5) = 1*prime(1) * 2*prime(2) * 3*prime(3) * 5*prime(5).

MATHEMATICA

a[n_] := Times @@ (PrimePi[#[[1]]] #[[1]] & /@ FactorInteger[n]); a[1] = 1; Select[Range[200000], a[#] == # &]

PROG

(PARI) isok(n) = {my(f=factor(n)); prod(k=1, #f~, primepi(f[k, 1])*f[k, 1]) == n; } \\ Michel Marcus, May 08 2018

CROSSREFS

Cf. A000720, A003557, A005117, A007947, A008478, A033286, A046022, A048768, A078779, A109298, A156061.

Sequence in context: A375885 A342319 A127214 * A124723 A122229 A285146

Adjacent sequences: A304191 A304192 A304193 * A304195 A304196 A304197

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, May 07 2018

STATUS

approved