A081870 a(1)=1, a(n)=2*a(n-1)+1 if that number is not squarefree, a(n)=a(n-1)+1 otherwise.

1, 2, 3, 4, 9, 10, 11, 12, 25, 26, 27, 28, 29, 30, 31, 63, 64, 65, 66, 67, 135, 136, 137, 275, 276, 277, 278, 279, 280, 281, 282, 283, 567, 568, 569, 570, 571, 1143, 1144, 1145, 1146, 1147, 2295, 2296, 2297, 2298, 2299, 4599, 4600, 4601, 4602, 4603, 9207, 9208

Offset

1,2

Links

Ivan Neretin, Table of n, a(n) for n = 1..750

Formula

a(n)=r(n)*2^b(n) where b(n) is an integer sequence and r(n) converges to 1.124922752241150441104513529....

Mathematica

NestList[If[SquareFreeQ[2 # + 1], # + 1, 2 # + 1] &, 1, 53] (* Ivan Neretin, Apr 26 2017 *)

Crossrefs

Sequence in context: A265746 A047454 A373788 * A165315 A284681 A309346

Adjacent sequences: A081867 A081868 A081869 * A081871 A081872 A081873

Keyword

nonn

Author

Benoit Cloitre, Apr 12 2003

Status

approved