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A124740 a(n) = product of those positive integers which are coprime to both n and n+1 and which are <= n. 5

%I #9 Oct 11 2019 10:59:16

%S 1,1,1,3,1,5,15,35,7,189,35,385,1485,143,1001,2027025,5005,85085,

%T 459459,46189,20995,1249937325,1616615,7436429,324342711,71504125,

%U 132793375,1452095555625,7436429,215656441,6190283353629375,75969882625

%N a(n) = product of those positive integers which are coprime to both n and n+1 and which are <= n.

%e The positive integers which are coprime to 8 and which are <= 8 are 1,3,5,7. The positive integers which are coprime to 9 and which are <= 9 are 1, 2,4,5,7,8. The integers in both these sequences (1,5,7) are multiplied to get a(8) = 35.

%t f[n_] := Times @@ Select[Range[n], GCD[n, # ] == GCD[n + 1, # ] == 1 &];Table[f[n], {n, 33}] (* _Ray Chandler_, Nov 10 2006 *)

%Y Cf. A057475, A124738, A124739, A124741.

%K nonn

%O 1,4

%A _Leroy Quet_, Nov 06 2006

%E Extended by _Ray Chandler_, Nov 10 2006

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Last modified March 29 05:16 EDT 2024. Contains 371264 sequences. (Running on oeis4.)