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a(n) = ((sqrt(2); sqrt(2))_n + (-sqrt(2); -sqrt(2))_n)/2, where (q; q)_n is the q-Pochhammer symbol.
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%I #26 Feb 13 2018 05:58:46

%S 1,1,-1,-5,15,87,-609,-8337,125055,2695455,-83559105,-4212669825,

%T 265398198975,22347926076735,-2838186611745345,-560679228377509185,

%U 142973203236264842175,47858338570309251530175,-24455611009428027531919425,-19225279650279123532147010625

%N a(n) = ((sqrt(2); sqrt(2))_n + (-sqrt(2); -sqrt(2))_n)/2, where (q; q)_n is the q-Pochhammer symbol.

%C The q-Pochhammer symbol (q; q)_n = Product_{k=1..n} (1 - q^k).

%H G. C. Greubel, <a href="/A276474/b276474.txt">Table of n, a(n) for n = 0..114</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/q-PochhammerSymbol.html">q-Pochhammer Symbol</a>.

%F (sqrt(2); sqrt(2))_n = a(n) + A276475(n)*sqrt(2).

%F (-sqrt(2); -sqrt(2))_n = a(n) - A276475(n)*sqrt(2).

%t Round@Table[(QPochhammer[Sqrt[2], Sqrt[2], n] + QPochhammer[-Sqrt[2], -Sqrt[2], n])/2, {n, 0, 20}]

%Y Cf. A276475, A263687, A263688.

%K sign

%O 0,4

%A _Vladimir Reshetnikov_, Sep 12 2016