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A103161
GCD of reverse(2^n) and reverse(2^(n+1)), where reverse(k) = A004086(k), the decimal representation of k 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
OFFSET
1,1
LINKS
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
Sequence in context: A236367 A197489 A297966 * A338000 A030420 A133902
KEYWORD
base,nonn
AUTHOR
Labos Elemer, Jan 25 2005
STATUS
approved