A139280 a(n) = 90*n - 81.

9, 99, 189, 279, 369, 459, 549, 639, 729, 819, 909, 999, 1089, 1179, 1269, 1359, 1449, 1539, 1629, 1719, 1809, 1899, 1989, 2079, 2169, 2259, 2349, 2439, 2529, 2619, 2709, 2799, 2889, 2979, 3069, 3159, 3249, 3339, 3429, 3519, 3609, 3699, 3789, 3879, 3969

Offset: 1

Author

Odimar Fabeny, Jun 06 2008

Keywords

• easy
• nonn

Comments

Multiples of 9 with final digit 9.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..2000
• Index entries for linear recurrences with constant coefficients, signature (2,-1).

Crossrefs

Subsequence of A034709, together with A017281, A017293, A139222, A139245, A017329, A139249, A139264 and A139279.

Cf. A017281, A139222.

Programs

Magma

[90*n-81: n in [1..50]]; // Vincenzo Librandi, Jun 19 2011

Mathematica

Table[90*n-81, {n, 0, 50}] (* G. C. Greubel, Jul 18 2017 *)

PARI

for(n=1, 1e2, a=90*n-81; print1(a, ", ")) \\ Felix Fröhlich, Jul 07 2014

Formula

a(n) = a(n-1) + 90.

From G. C. Greubel, Jul 18 2017: (Start)

G.f.: 9*(19*x-9)/(x-1)^2.

E.g.f.: 81 + 9*(10*x - 9)*exp(x). (End) [G.f. corrected by Georg Fischer, May 12 2019]; [E.g.f. corrected by Elmo R. Oliveira, Apr 04 2025]

From Elmo R. Oliveira, Apr 04 2025: (Start)

a(n) = 9*A017281(n-1) = 3*A139222(n).

a(n) = 2*a(n-1) - a(n-2) for n > 2. (End)

Extensions

More terms from Reinhard Zumkeller, Jun 22 2008