A377864 Largest divisor of 2n-1 less than or equal to sqrt(2n-1).

1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 5, 3, 1, 1, 3, 5, 1, 3, 1, 1, 5, 1, 7, 3, 1, 5, 3, 1, 1, 7, 5, 1, 3, 1, 1, 5, 7, 1, 9, 1, 5, 3, 1, 7, 3, 5, 1, 9, 1, 1, 7, 1, 1, 3, 1, 5, 9, 7, 11, 3, 5, 1, 3, 1, 7, 9, 1, 1, 3, 11, 5, 7, 1, 1, 9, 5, 1, 3, 7, 1, 11, 1, 13, 9

Offset: 1

Author

Charles Kusniec, Nov 10 2024

Keywords

• nonn
• easy

Crossrefs

Odd bisection of A033676.

Cf. A377499, A219695.

Programs

Mathematica

a[n_]:=Module[{k=2n-1},While[!Divisible[2n-1,k] || k>Sqrt[2n-1] ,k--]; k]; Array[a,86] (* Stefano Spezia, Nov 17 2024 *)

PARI

a(n) = {my(d = divisors(2*n-1)); d[ceil(#d/2)]} \\ Thomas Scheuerle, Nov 17 2024

Formula

a(n) = A033676(2n-1).

a(n) = A377499(n) - A219695(n).