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EXAMPLE
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G.f.: A(x) = 1 + x + x^2 + x^3 + 3*x^4 + 8*x^5 + 26*x^6 + 89*x^7 + 324*x^8 +...
Form a table of coefficients in A(x)^(2*n) as follows:
[1, 0, 0, 0, 0, 0, 0, 0, 0, 0, ...];
[1, 2, 3, 4, 9, 24, 75, 252, 903, 3376, ...];
[1, 4, 10, 20, 43, 108, 316, 1020, 3537, 12908, ...];
[1, 6, 21, 56, 138, 354, 1002, 3120, 10485, 37318, ...];
[1, 8, 36, 120, 346, 960, 2756, 8448, 27723, 96440, ...];
[1, 10, 55, 220, 735, 2252, 6785, 21020, 68340, 233870, ...];
[1, 12, 78, 364, 1389, 4716, 15184, 48588, 159186, 541424, ...];
[1, 14, 105, 560, 2408, 9030, 31304, 104960, 351792, 1203244, ...];
[1, 16, 136, 816, 3908, 16096, 60184, 213152, 739162, 2570464, ...];
[1, 18, 171, 1140, 6021, 27072, 109047, 409500, 1480293, 5280932, ...]; ...
then the main diagonal forms the Franel numbers:
[1, 2, 10, 56, 346, 2252, 15184, 104960, 739162, 5280932, ...].
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