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

Offset: 1

Author

Amarnath Murthy, Mar 30 2002

Keywords

• nonn
• easy

Comments

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

Links

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

Crossrefs

Cf. A000217, A008592.

Programs

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);

Mathematica

Select[Accumulate[Range[0,250]],Divisible[#,10]&] (* Harvey P. Dale, Aug 28 2016 *)

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

Extensions

Corrected and extended by Harvey P. Dale and Sascha Kurz, Mar 31 2002