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A103161 GCD of reversed(2^n) and reversed(2^(n+1)), where reversed = A004086, the decimal representation of n read backwards. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified June 18 11:58 EDT 2021. Contains 345098 sequences. (Running on oeis4.)