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A001526
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a(n) = (7*n+1)*(7*n+6).
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1
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6, 104, 300, 594, 986, 1476, 2064, 2750, 3534, 4416, 5396, 6474, 7650, 8924, 10296, 11766, 13334, 15000, 16764, 18626, 20586, 22644, 24800, 27054, 29406, 31856, 34404, 37050, 39794, 42636, 45576, 48614, 51750, 54984, 58316, 61746, 65274, 68900, 72624, 76446
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listen;
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OFFSET
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0,1
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LINKS
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FORMULA
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Sum_{n>=0} 1/a(n) = cot(Pi/7)*Pi/35.
Product_{n>=0} (1 - 1/a(n)) = cosec(Pi/7)*cos(sqrt(29)*Pi/14).
Product_{n>=0} (1 + 1/a(n)) = cosec(Pi/7)*cos(sqrt(3/7)*Pi/2). (End)
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MATHEMATICA
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a[n_] := (7*n + 1)*(7*n + 6); Array[a, 40, 0] (* Amiram Eldar, Feb 19 2023 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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