A081870 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

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

(list; graph; refs; listen; history; text; internal format)

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