A382769 Largest k < n such that gcd(k,n) > 1 and rad(k) does not divide n, where rad = A007947, or 0 if k does not exist.

0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 10, 0, 12, 12, 0, 0, 15, 0, 18, 18, 20, 0, 22, 0, 24, 0, 26, 0, 28, 0, 0, 30, 30, 30, 34, 0, 36, 36, 38, 0, 40, 0, 42, 42, 44, 0, 46, 0, 48, 48, 50, 0, 52, 50, 54, 54, 56, 0, 58, 0, 60, 60, 0, 60, 63, 0, 66, 66, 68, 0, 70, 0, 72

Offset

1,10

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Formula

a(n) = 0 for n = 6, and n in A000961.

For n > 6 in A024619, a(n) is the last term in row n of A272619.

Mathematica

rad[x_] := rad[x] = Times @@ FactorInteger[x][[All, 1]]; {0}~Join~Table[If[Nor[PrimePowerQ[n], n == 6], k = n - 2; While[Or[CoprimeQ[n, k], Divisible[n, rad[k]]], k--]; k, 0], {n, 2, 120}]

Crossrefs

Cf. A000961, A024619, A096014, A272619.

Sequence in context: A019622 A187429 A083573 * A117006 A294345 A073764

Adjacent sequences: A382766 A382767 A382768 * A382770 A382771 A382772

Keyword

nonn,easy

Author

Michael De Vlieger, Apr 04 2025

Status

approved