A233089 Numbers n such that 2n-1 and 2n+1 divide 2^n-1.

8, 128, 228, 648, 3240, 5976, 13160, 23760, 23940, 24840, 32768, 37224, 78540, 82800, 139248, 166716, 238368, 278520, 280368, 288360, 516528, 633420, 664668, 731808, 734448, 1145520, 1211100, 1377240, 1425816, 1484568, 1627640, 2055060, 2131080, 2292780

Offset: 1

Author

Michel Marcus, Dec 04 2013

Keywords

• nonn

Comments

Intersection of A081856 and A081858.

Numbers n such that 4n^2-1 divides 2^n-1. - Charles R Greathouse IV, Dec 04 2013

Examples

			2^8-1=255 is divisible by 2*8-1=15 and by 2*8+1=17.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..5000

Programs

Mathematica

Select[Range[23*10^5],PowerMod[2,#,2#+{1,-1}]=={1,1}&] (* Harvey P. Dale, Dec 19 2014 *)

PARI

isok(n) = !((2^n-1) % (2*n-1)) && !((2^n-1) % (2*n+1));

PARI

is(n)=Mod(2,4*n^2-1)^n==1 \\ Charles R Greathouse IV, Dec 04 2013