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A256918 Greatest common divisors of adjacent terms in A257218.

%I A256918 #36 Apr 26 2015 00:14:48
%S A256918 1,1,3,2,4,2,5,5,3,9,6,4,8,6,10,20,8,16,12,9,27,18,12,15,15,25,25,10,
%T A256918 7,7,14,14,21,21,63,42,28,56,16,32,24,40,20,50,30,18,27,81,54,72,24,
%U A256918 28,35,35,105,30,45,45,75,100,40,32,64,48,48,36,63,189
%N A256918 Greatest common divisors of adjacent terms in A257218.
%C A256918 a(n) = GCD(A257218(n),A257218(n+1)).
%C A256918 Each term occurs at most twice, and it is a plausible conjecture that every term will occur exactly twice.
%C A256918 A257120(n) = position of the first of not more than two occurrences of n: a(A257120(n)) = n;
%C A256918 A257475(n) = position of the second and last occurrence of n: a(A257475(n)) = n;
%C A256918 A257478(n) = distance of positions of first and second occurrence of n.
%H A256918 Reinhard Zumkeller, <a href="/A256918/b256918.txt">Table of n, a(n) for n = 1..25000</a>
%o A256918 (Haskell)
%o A256918 a256918 n = a257218_list !! (n-1)
%o A256918 a256918_list = zipWith gcd a257218_list $ tail a257218_list
%Y A256918 Cf. A257218, A257120, A257475, A257478.
%K A256918 nonn
%O A256918 1,3
%A A256918 _Reinhard Zumkeller_, Apr 25 2015