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A077261 Triangular numbers that are 5x another triangular number. 4
0, 15, 105, 4950, 33930, 1594005, 10925475, 513264780, 3517969140, 165269665275, 1132775137725, 53216318953890, 364750076378430, 17135489433487425, 117448391818716855, 5517574381263997080, 37818017415550449000, 1776641815277573572455, 12177284159415425861265 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The triangular numbers that are 1/5 are in A077260.

LINKS

Colin Barker, Table of n, a(n) for n = 0..797

Index entries for linear recurrences with constant coefficients, signature (1,322,-322,-1,1).

FORMULA

Let b(n)=A077260 then a(n)=5*b(n).

G.f.:(-15*x*(x^2+6*x+1))/((x-1)*(x^2-18*x+1)*(x^2+18*x+1)). - Maksym Voznyy (voznyy(AT)mail.ru), Jul 27 2009

EXAMPLE

a(3)=5*990=4950.

CROSSREFS

Cf. A077259, A077260, A077262.

Sequence in context: A264415 A319588 A165892 * A012507 A143727 A231327

Adjacent sequences:  A077258 A077259 A077260 * A077262 A077263 A077264

KEYWORD

easy,nonn

AUTHOR

Bruce Corrigan (scentman(AT)myfamily.com), Nov 01 2002

STATUS

approved

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Last modified November 18 22:39 EST 2019. Contains 329305 sequences. (Running on oeis4.)