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A125596 a(1)=1. a(n) = Sum_{1<=k<n, gcd(k,n(n+1))=1} a(k). 1
1, 1, 1, 2, 1, 2, 3, 5, 4, 9, 5, 10, 12, 18, 21, 48, 22, 44, 48, 88, 84, 197, 92, 183, 260, 432, 441, 908, 183, 366, 1178, 1800, 1778, 3743, 1541, 3346, 5627, 8913, 7159, 16638, 7429, 14858, 24107, 38702, 38615, 88520, 40509, 79474, 88596, 167790, 169580 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,4
LINKS
EXAMPLE
The positive integers < 8 and coprime to 8 and 9 are 1,5,7. So a(8) = a(1) + a(5) + a(7) = 1+1+3 = 5.
MATHEMATICA
f[l_List] := Block[{n = Length[l] + 1}, Append[l, Plus @@ l[[Select[Range[n], GCD[ #, n*(n + 1)] == 1 &]]]]]; Nest[f, {1}, 50] (* Ray Chandler, Nov 26 2006 *)
CROSSREFS
Cf. A125597.
Sequence in context: A106436 A363226 A075758 * A351962 A253026 A341145
KEYWORD
nonn
AUTHOR
Leroy Quet, Nov 26 2006
EXTENSIONS
Extended by Ray Chandler, Nov 26 2006
STATUS
approved

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Last modified May 29 00:29 EDT 2024. Contains 372921 sequences. (Running on oeis4.)