OFFSET
1,1
COMMENTS
The asymptotic density of this sequence is Product_{p prime} (1 - 1/p^4 + Sum_{q prime >= 5} 1/p^q - 1/p^(q-1)) = 0.05328066264472198953... (using the method of Shevelev, 2016). - Amiram Eldar, Nov 08 2020
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
Vladimir Shevelev, A fast computation of density of exponentially S-numbers, arXiv:1602.04244 [math.NT], 2016.
EXAMPLE
16 = 2^4 is a term because 4 is a composite exponent here.
MAPLE
a:= proc(n) option remember; local k; for k from 1+
`if`(n=1, 0, a(n-1)) while andmap(i-> i[2]=1 or
isprime(i[2]), ifactors(k)[2]) do od; k
end:
seq(a(n), n=1..70);
MATHEMATICA
Select[Range[1000], AnyTrue[FactorInteger[#][[;; , 2]], CompositeQ] &] (* Amiram Eldar, Nov 08 2020 *)
PROG
(PARI) isok(m) = #select(x->((x>1) && !isprime(x)), factor(m)[, 2]) > 0; \\ Michel Marcus, Dec 02 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Dec 08 2018
STATUS
approved