OFFSET
1,1
COMMENTS
Proper subsequence of A126706.
Numbers k such that there does not exist j such that 1 < j < k and rad(j) = rad(k), but j does not divide k.
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1) = 12, since 12/6 < 3.
a(2) = 20, since 20/10 < 5.
a(3) = 28, since 28/14 < 7.
a(4) = 40, since 40/10 < 5, etc.
MATHEMATICA
Select[Select[Range[120], Nor[SquareFreeQ[#], PrimePowerQ[#]] &], #1/#2 < #3 & @@ {#1, Times @@ #2, #2[[2]]} & @@ {#, FactorInteger[#][[All, 1]]} &]
PROG
(PARI) rad(n) = factorback(factorint(n)[, 1]); \\ A007947
f(n) = if (isprimepower(n) || (n==1), 1, my(f=factor(n)[, 1]); f[2]); \\ A119288
isok(k) = !isprimepower(k) && !issquarefree(k) && (k/rad(k) < f(k)); \\ Michel Marcus, Mar 01 2023
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Michael De Vlieger, Feb 28 2023
STATUS
approved