A072033 Smallest x > 0 such that gcd(2^x, A004086(2^x)) = 2^n.

4, 1, 2, 3, 26, 131, 227, 301, 567, 879, 3240, 11051, 8048, 38911, 7321, 97309, 108190, 6294, 138124, 4675268, 2687104, 1336154, 5774420

Offset: 1

Author

Labos Elemer, Jun 07 2002

Keywords

• nonn
• base
• more

Comments

a(14)=7321, a(17)=6294.

Examples

			n=4: a(4)=26 because gcd(2^26, reverse(2^26)) = gcd(67108864, 46880176) = 16 = 2^n.
		

Crossrefs

Cf. A055483, A004086, A071686, A072032.

Programs

Mathematica

a[n_] := Block[{k=1}, While[ IntegerExponent[ GCD[2^k, FromDigits@ Reverse@ IntegerDigits[2^k]], 2] != n, k++]; k]; Array[a, 13, 0] (* Giovanni Resta, Oct 28 2019 *)

Formula

a(n) = min{x: gcd(2^x, reverse(2^x))=2^n} = min{x: A055483(x)=2^n}.

A072032(a(n)) = 2^n.

Extensions

Offset corrected, missing a(3) and a(13)-a(22) added by Giovanni Resta, Oct 28 2019