A103161 GCD of reverse(2^n) and reverse(2^(n+1)), where reverse(k) = A004086(k), the decimal representation of k read backwards.

2, 4, 1, 1, 23, 1, 1, 1, 1, 4201, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 1, 7, 1, 1, 1, 1, 4, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 19, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4, 1, 1, 1, 1, 1, 1, 1, 1, 1, 34, 1, 1, 1, 7, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1

Offset

1,1

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Formula

a(n) = gcd(A004094(n), A004094(n+1)).

Example

n=10: GCD of backward written powers of 2 is GCD(4201, 8402) = 4201 = a(10).

Mathematica

rd[x_] :=FromDigits[Reverse[IntegerDigits[x]]] Table[GCD[rd[2^w], rd[2^(w+1)]], {w, 1, 100}]
GCD[IntegerReverse[#[[1]]], IntegerReverse[#[[2]]]]&/@ Partition[ 2^Range[110], 2, 1] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 24 2017 *)

Prog

(PARI)
rev(n) = subst(Polrev(digits(n)), 'x, 10); \\ These two functions from Charles R Greathouse IV, Oct 20 2014
A004094(n) = rev(2^n);
A103161(n) = gcd(A004094(n), A004094(1+n)); \\ Antti Karttunen, Dec 07 2017

Crossrefs

Cf. A000079, A004094.

Sequence in context: A236367 A197489 A297966 * A338000 A030420 A133902

Adjacent sequences: A103158 A103159 A103160 * A103162 A103163 A103164

Keyword

base,nonn

Author

Labos Elemer, Jan 25 2005

Status

approved