OFFSET

1,2

COMMENTS

LINKS

FORMULA

Sum_{n>=1} 1/a(n) = Sum_{k>=2} (-1)^k * s(k) = 1.65243302848832032223..., where s(k) = Product_{p prime} (1 + Sum_{i=2..k} 1/p^i).

MATHEMATICA

seq[lim_] := Select[Union@ Flatten@ Table[i^2 * j^3, {j, 1, Surd[lim, 3]}, {i, 1, Sqrt[lim/j^3]}], # == 1 || EvenQ[Max[FactorInteger[#][[;; , 2]]]] &]; seq[10^4]

PROG

(PARI) is(k) = {my(f = factor(k), e = f[, 2]); !(#e) || (ispowerful(f) && !(vecmax(e) % 2)); }

CROSSREFS

KEYWORD

nonn,easy

AUTHOR

Amiram Eldar, Sep 13 2024

STATUS

approved