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A171080 a(n) = Product_{3 <= q <= 2n+1, q prime} q^floor((2n/(q-1)). 4

%I

%S 1,3,45,945,14175,467775,638512875,1915538625,488462349375,

%T 194896477400625,32157918771103125,2218896395206115625,

%U 3028793579456347828125,9086380738369043484375,3952575621190533915703125,28304394023345413370350078125,7217620475953080409439269921875

%N a(n) = Product_{3 <= q <= 2n+1, q prime} q^floor((2n/(q-1)).

%D F. Hirzebruch, Topological Methods in Algebraic Geometry, Springer, 3rd. ed., 1966; Lemma 1.5.2, p. 13.

%p f:=proc(n) local q,t1; t1:=1; for q from 3 to 2*n+1 do if isprime(q) then t1:=t1*q^floor(2*n/(q-1)); fi; od; t1; end;

%t a[n_] := Product[If[PrimeQ[q], q^Floor[2 n/(q - 1)], 1], {q, 3, 2 n + 1}]

%t Table[a[n],{n,0,20}] (* _Wolfgang Hintze_, Oct 03 2014 *)

%Y Cf. A091137

%K nonn

%O 0,2

%A _N. J. A. Sloane_, Sep 06 2010

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Last modified May 28 22:08 EDT 2022. Contains 354122 sequences. (Running on oeis4.)