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A127431 a(1)=1. a(n) = number of earlier terms a(k), 1<=k<=n-1, such that (k+n) is divisible by a(k). 3

%I #13 Jul 23 2020 19:27:02

%S 1,1,2,2,3,3,4,3,5,5,4,4,7,3,6,8,5,5,6,5,8,8,5,6,10,5,8,8,9,7,7,8,9,9,

%T 8,9,12,5,8,12,8,9,10,7,13,9,13,11,10,7,9,12,11,9,11,10,18,8,8,10,16,

%U 10,9,12,11,11,14,13,13,12,10,15,12,10,15,11,15,12,11,13,14,12,12,13,18,9,14

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

%H Rémy Sigrist, <a href="/A127431/b127431.txt">Table of n, a(n) for n = 1..10000</a>

%H Rémy Sigrist, <a href="/A127431/a127431.txt">C program for A127431</a>

%e (1+11) is a multiple of a(1)=1; (2+11) is a multiple of a(2)=1; (3+11) is a multiple of a(3)=2; and (9+11) is a multiple of a(9)=5. These four cases are the only cases where (k+n) is divisible by a(k), for 1<=k<=10. So a(11) = 4.

%t f[l_List] := Block[{n = Length[l] + 1},Append[l, Count[Table[Mod[k + n, l[[k]]], {k, n - 1}], 0]]];Nest[f, {1}, 86] (* _Ray Chandler_, Jan 22 2007 *)

%o (C) See Links section.

%Y Cf. A127432, A127433.

%K nonn,look

%O 1,3

%A _Leroy Quet_, Jan 14 2007

%E Extended by _Ray Chandler_, Jan 22 2007

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Last modified March 1 14:57 EST 2024. Contains 370433 sequences. (Running on oeis4.)