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A077260
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Triangular numbers that are 1/5 of a triangular number.
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3
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0, 3, 21, 990, 6786, 318801, 2185095, 102652956, 703593828, 33053933055, 226555027545, 10643263790778
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| The triangular numbers 5x these are in A077261
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FORMULA
| Let b(n)=A077259(n) then a(n)=b(n)*(b(n)+1)/2
a(n) = (A000045(A007310(n+1))^2-1)/8. - Vladeta Jovovic (vladeta(AT)eunet.rs), Nov 02 2002. [Definition corrected by R. J. Mathar, Sep 16 2009]
G.f.:(-3*x*(x^2+6*x+1))/((x-1)*(x^2-18*x+1)*(x^2+18*x+1)) [From Maksym Voznyy (voznyy(AT)mail.ru), Jul 27 2009]
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EXAMPLE
| Since b(3)=44 -> a(3)=44*45/2=990
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CROSSREFS
| Cf. A077259, A077261, A077262.
Sequence in context: A111435 A111438 A058635 * A012110 A054739 A117508
Adjacent sequences: A077257 A077258 A077259 * A077261 A077262 A077263
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KEYWORD
| easy,nonn
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AUTHOR
| Bruce Corrigan (scentman(AT)myfamily.com), Nov 01 2002
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