A304253 Numbers k such that k = Product (p_j^e_j) = Sum (prime(p_j)^e_j).

20, 68, 76, 92, 8248

Offset: 1

Author

Ilya Gutkovskiy, May 09 2018

Keywords

• nonn
• more

Comments

Fixed points of A304251.

Examples

			68 is a term because 68 = 2^2*17 = prime(1)^2*prime(7) = prime(prime(1))^2 + prime(prime(7)).
8248 is a term because 8248 = 2^3*1031 = prime(1)^3*prime(173) = prime(prime(1))^3 + prime(prime(173)).
		

Links

• Index entries for sequences computed from indices in prime factorization

Crossrefs

Cf. A006450, A008478, A048768, A304194, A304251.

Programs

Mathematica

a[n_] := Plus @@ (Prime[#[[1]]]^#[[2]] & /@ FactorInteger[n]); Select[Range[10000], a[#] == # &]

PARI

isok(n) = my(f=factor(n)); n == sum(k=1, #f~, prime(f[k,1])^f[k,2]); \\ Michel Marcus, May 09 2018