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%I #10 Aug 02 2019 20:10:55
%S 1,1,2,3,19,25,12091,942579,802405765442,9728923151534907,
%T 40387361143971542769608346059516047956596,
%U 16013133965687337121814734147004294320263129575
%N a(n) = numerator of b(n), where b(1)=1, b(n) = Sum_{1<=k<n, gcd(k,n)=1} 1/b(k).
%e {b(n)}: 1, 1, 2, 3/2, 19/6, 25/19, 12091/2850, ... Since 1 and 5 are the positive integers which are coprime to 6 and are < 6, b(6) = 1/b(1) + 1/b(5) = 1 + 6/19 = 25/19.
%t f[l_List] := Block[{n = Length[l] + 1, d},d = Select[Range[n - 1], GCD[ #, n] == 1 &];Append[l, Sum[1/l[[d[[i]]]], {i, Length[d]}]]];Numerator[Nest[f, {1}, 12]] (* _Ray Chandler_, Feb 09 2007 *)
%Y Cf. A127942.
%K frac,nonn
%O 1,3
%A _Leroy Quet_, Feb 08 2007
%E Extended by _Ray Chandler_, Feb 09 2007
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