OFFSET
1,6
COMMENTS
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
Michael De Vlieger, Scalar scatterplot of a(n) for n = 1..2^20.
Michael De Vlieger, Plot a(n) at (x,y) = (n mod 210, -floor(n/210)) for n = 1..44100, showing 0 in light gray, perfect prime powers (a(n) in A246547) in gold, a(n) in A332785 in blue, and a(n) in A286708 in magenta.
EXAMPLE
a(6) = 4 since 4 is the largest nondivisor k in S(6) = {1, 2, 3, 4, 6}.
a(10) = 8 since 8 is the largest nondivisor k in S(10) = {1, 2, 4, 5, 8, 10}.
a(15) = 9 since 9 is the largest nondivisor k in S(15) = {1, 3, 5, 9, 15}, etc.
MATHEMATICA
rad[x_] := rad[x] = Times @@ FactorInteger[x][[All, 1]];
Table[If[PrimePowerQ[n], 0, k = n - 1; Until[And[Divisible[n, rad[k]], ! Divisible[n, k]], k--]; k], {n, 2, 120}]
PROG
(PARI) rad(n) = factorback(factorint(n)[, 1]);
a(n) = forstep(k=n-1, 1, -1, if ((n % k) && !(n % rad(k)), return(k))); \\ Michel Marcus, Jun 18 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael De Vlieger, Jun 18 2024
STATUS
approved