A394210 a(n) is the least k > 1 such that gpf(2^n*k) > gpf(2^n*k-1) where gpf is the greatest prime factor (A006530).

5, 7, 17, 11, 23, 19, 19, 26, 13, 67, 47, 47, 59, 89, 197, 137, 158, 79, 383, 331, 393, 769, 487, 467, 347, 1009, 1697, 1021, 1059, 2458, 1229, 997, 1478, 739, 1718, 859, 6126, 3063, 4481, 6211, 10567, 6469, 11912, 5956, 2978, 1489, 5942, 2971, 4001, 4091

Offset

1,1

Links

Table of n, a(n) for n=1..50.

Example

a(3)=17 because 2^3*17-1=136-1=135 has 5 as its largest prime factor.

Mathematica

a[n_]:=Module[{k=2^n}, While[Max[First/@FactorInteger[k]]<=(m=Max[First/@FactorInteger[k-1]])||!PrimeQ[m], k+=2^n]; k/2^n]; Array[a, 30] (* Stefano Spezia, Apr 09 2026 *)

Crossrefs

Cf. A000079, A006530.

Sequence in context: A185872 A186710 A276717 * A374777 A318491 A060640

Adjacent sequences: A394207 A394208 A394209 * A394211 A394212 A394213

Keyword

nonn,easy

Author

J. Lowell, Apr 09 2026

Extensions

More terms from David A. Corneth, Apr 09 2026

Status

approved