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 A127434 a(0)=1. a(n) = number of earlier terms a(k), 0<=k<=n-1, such that (k+n) is coprime to a(k). 3

%I #11 Jul 23 2020 19:29:49

%S 1,1,2,3,3,4,4,6,4,6,7,6,7,9,8,10,10,10,9,12,10,12,15,11,14,14,14,16,

%T 17,15,16,20,16,19,21,19,20,23,19,22,25,23,27,26,25,27,31,29,28,33,29,

%U 29,37,33,34,37,33,35,37,38,36,42,38,41,43,36,41,46,42,43,47,44,46,49,42

%N a(0)=1. a(n) = number of earlier terms a(k), 0<=k<=n-1, such that (k+n) is coprime to a(k).

%H Rémy Sigrist, <a href="/A127434/b127434.txt">Table of n, a(n) for n = 0..10000</a>

%H Rémy Sigrist, <a href="/A127434/a127434.txt">C program for A127434</a>

%e (0+9) is coprime to a(0)=1; (1+9) is coprime to a(1)=1; (2+9) is coprime to a(2)=2; (4+9) is coprime to a(4)=3, (6+9) is coprime to a(6)=4; and (8+9) is coprime to a(8)=4. These six cases are the only cases where (k+n) is coprime to a(k), for 0<=k<=8. So a(9) = 6.

%t f[l_List] := Block[{n = Length[l]},Append[l, Count[Table[GCD[k + n - 1, l[[k]]], {k, n}], 1]]];Nest[f, {1}, 75] (* _Ray Chandler_, Jan 22 2007 *)

%Y Cf. A127432, A127433.

%K nonn

%O 0,3

%A _Leroy Quet_, Jan 14 2007

%E Extended by _Ray Chandler_, Jan 22 2007

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Last modified December 7 04:15 EST 2023. Contains 367629 sequences. (Running on oeis4.)