A081553 Sum of n-th row of A081551.

1, 21, 303, 4006, 50010, 600015, 7000021, 80000028, 900000036, 10000000045, 110000000055, 1200000000066, 13000000000078, 140000000000091, 1500000000000105, 16000000000000120, 170000000000000136, 1800000000000000153, 19000000000000000171, 200000000000000000190, 2100000000000000000210, 22000000000000000000231

Offset

1,2

Links

G. C. Greubel, Table of n, a(n) for n = 1..500

Index entries for linear recurrences with constant coefficients, signature (23,-163,361,-320,100).

Formula

a(n) = n*10^(n-1) + n*(n-1)/2.

From G. C. Greubel, May 27 2021: (Start)

G.f.: x*(1 -2*x -17*x^2 +99*x^3)/((1-x)^3 * (1-10*x)^2).

E.g.f.: (1/2)*x*( x*exp(x) + 2*exp(10*x) ). (End)

Mathematica

Table[n*10^(n-1) +n(n-1)/2, {n, 40}] (* G. C. Greubel, May 27 2021 *)

Prog

(Sage) [n*10^(n-1) +binomial(n, 2) for n in (1..40)] # G. C. Greubel, May 27 2021

Crossrefs

Cf. A081551, A081552.

Cf. A126431, A161680.

Sequence in context: A079517 A021784 A019618 * A021524 A021268 A018069

Adjacent sequences: A081550 A081551 A081552 * A081554 A081555 A081556

Keyword

base,easy,nonn

Author

Amarnath Murthy, Apr 01 2003

Extensions

Terms a(13) onward added by G. C. Greubel, May 27 2021

Status

approved