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A014771
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Squares of odd hexagonal numbers.
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1
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1, 225, 2025, 8281, 23409, 53361, 105625, 189225, 314721, 494209, 741321, 1071225, 1500625, 2047761, 2732409, 3575881, 4601025, 5832225, 7295401, 9018009, 11029041, 13359025, 16040025, 19105641, 22591009, 26532801, 30969225, 35940025, 41486481, 47651409
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OFFSET
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1,2
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LINKS
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FORMULA
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G.f.: x*(1+220*x+910*x^2+396*x^3+9*x^4)/(1-x)^5. - Maksym Voznyy (voznyy(AT)mail.ru), Aug 11 2009; checked and corrected by R. J. Mathar, Sep 16 2009
a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>5. - Harvey P. Dale, Jun 23 2011
Sum_{n>=1} 1/a(n) = 2*G + 3*Pi^2/8 - Pi - 2*log(2), where G is Catalan's constant (A006752). - Amiram Eldar, Feb 27 2022
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MAPLE
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MATHEMATICA
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(Select[Table[n(2n-1), {n, 60}], OddQ])^2 (* or *) LinearRecurrence[ {5, -10, 10, -5, 1}, {1, 225, 2025, 8281, 23409}, 30] (* Harvey P. Dale, Jun 23 2011 *)
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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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EXTENSIONS
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STATUS
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approved
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