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A076767
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Triangular numbers with square pyramidal indices.
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0
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0, 1, 15, 105, 465, 1540, 4186, 9870, 20910, 40755, 74305, 128271, 211575, 335790, 515620, 769420, 1119756, 1594005, 2224995, 3051685, 4119885, 5483016, 7202910, 9350650, 12007450, 15265575, 19229301, 24015915, 29756755, 36598290
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OFFSET
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0,3
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LINKS
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Table of n, a(n) for n=0..29.
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
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FORMULA
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let SP(m) be the m-th square pyramidal number m*(m+1)*(2*m+1)/6 and T(k) be the k-th Triangular number k*(k+1)/2 then a(n)=T(SP(n)).
G.f.: x*(1+8*x+21*x^2+10*x^3)/(1-x)^7. [Colin Barker, Apr 30 2012]
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EXAMPLE
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SP(3)=14 -> a(3)=T(SP(3))=T(14)=105; SP(4)=30 -> a(4)=T(SP(4))=T(30)=465 etc
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CROSSREFS
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Cf. A077538.
Sequence in context: A202288 A010931 A282350 * A022610 A006857 A000478
Adjacent sequences: A076764 A076765 A076766 * A076768 A076769 A076770
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KEYWORD
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easy,nonn
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AUTHOR
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Bruce Corrigan (scentman(AT)myfamily.com), Nov 14 2002
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STATUS
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approved
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