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A069498

Triangular numbers of the form 10*k.

0, 10, 120, 190, 210, 300, 630, 780, 820, 990, 1540, 1770, 1830, 2080, 2850, 3160, 3240, 3570, 4560, 4950, 5050, 5460, 6670, 7140, 7260, 7750, 9180, 9730, 9870, 10440, 12090, 12720, 12880, 13530, 15400, 16110, 16290, 17020, 19110, 19900, 20100, 20910, 23220

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OFFSET

1,2

COMMENTS

Intersection of A000217 and A008592. - Michel Marcus, Sep 17 2013

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (1,0,0,2,-2,0,0,-1,1).

FORMULA

G.f.: -10*x^2*(x^6+11*x^5+7*x^4+2*x^3+7*x^2+11*x+1) / ((x-1)^3*(x+1)^2*(x^2+1)^2). - Colin Barker, Sep 23 2013

MAPLE

a[0] := 0:a[1] := 4:a[2] := 15:a[3] := 19:seq((20*(floor(i/4))+a[i mod 4])*(20*(floor(i/4))+a[i mod 4]+1)/2, i=0..100);