A002281 a(n) = 7*(10^n - 1)/9.

0, 7, 77, 777, 7777, 77777, 777777, 7777777, 77777777, 777777777, 7777777777, 77777777777, 777777777777, 7777777777777, 77777777777777, 777777777777777, 7777777777777777, 77777777777777777, 777777777777777777, 7777777777777777777, 77777777777777777777, 777777777777777777777

Offset: 0

Author

N. J. A. Sloane

Keywords

• easy
• nonn

Links

• Ivan Panchenko, Table of n, a(n) for n = 0..200
• Index entries for linear recurrences with constant coefficients, signature (11,-10).

Crossrefs

Cf. A002275, A002276, A002277, A002278, A002279, A002280, A002282, A002283, A178630, A178634.

Cf. A010785, A017245, A099915.

Programs

Magma

[7*(10^n-1)/9 : n in [0..30]]; // Wesley Ivan Hurt, Mar 24 2015

Maple

A002281:=n->7*(10^n-1)/9: seq(A002281(n), n=0..30); # Wesley Ivan Hurt, Mar 24 2015

Mathematica

LinearRecurrence[{11,-10},{0,7},25] (* Robert G. Wilson v, Jul 06 2013 *)

PARI

a(n)=7*(10^n-1)/9 \\ Charles R Greathouse IV, Sep 24 2015

Formula

a(n) = A178634(n)/A002283(n). - Reinhard Zumkeller, May 31 2010

From Vincenzo Librandi, Jul 22 2010: (Start)

a(n) = a(n-1) + 7*10^(n-1) with n>0, a(0)=0.

a(n) = 11*a(n-1) - 10*a(n-2) with n>1, a(0)=0, a(1)=7. (End)

G.f.: 7*x/((x-1)*(10*x-1)). - Colin Barker, Jan 24 2013

a(n) = 7*A002275(n). - Wesley Ivan Hurt, Mar 24 2015

E.g.f.: 7*exp(x)*(exp(9*x) - 1)/9. - Stefano Spezia, Sep 13 2023

From Elmo R. Oliveira, Jul 20 2025: (Start)

a(n) = (A099915(n) - 1)/2.

a(n) = A010785(A017245(n-1)) for n >= 1. (End)