A391446 Numbers k such that gcd(A381466(k-1),k) > 1.

4, 8, 12, 14, 16, 20, 24, 27, 30, 32, 35, 38, 40, 44, 48, 50, 52, 54, 56, 58, 60, 62, 64, 68, 72, 75, 78, 80, 84, 87, 90, 92, 94, 96, 99, 102, 104, 108, 111, 114, 116, 118, 120, 123, 125, 128, 132, 135, 138, 140, 144, 146, 148, 150, 152, 154, 156, 158, 160

Offset

1,1

Comments

a(n) is the index of the n-th term in the lowest band of the graph of A381466.

a(n) is the n-th division step of A381466.

Links

Sam Chapman, Table of n, a(n) for n = 1..9999

Example

4 is a term because A381466(3) = 10, and (10,4) = 2 > 1.
8 is a term because A381466(7) = 20, and (20,8) = 4 > 1.

Mathematica

s={4}; k={}; Do[G=GCD[s[[-1]], n]; AppendTo[s, If[G==1, s[[-1]]+n, n/G]]; If[G>1, AppendTo[k, n]], {n, 160}]; k (* James C. McMahon, Apr 01 2026 *)

Crossrefs

Cf. A381466.

Sequence in context: A311078 A328303 A311079 * A257221 A092453 A285374

Adjacent sequences: A391443 A391444 A391445 * A391447 A391448 A391449

Keyword

nonn,changed

Author

Sam Chapman, Mar 18 2026

Status

approved