A173193 a(n) = (2*10^n + 43)/9.

7, 27, 227, 2227, 22227, 222227, 2222227, 22222227, 222222227, 2222222227, 22222222227, 222222222227, 2222222222227, 22222222222227, 222222222222227, 2222222222222227, 22222222222222227, 222222222222222227, 2222222222222222227, 22222222222222222227, 222222222222222222227

Offset: 1

Author

Ivan Panchenko, Feb 12 2010

Keywords

• easy
• nonn

Comments

n-1 2's followed by a 7.

Links

• Markus Tervooren, Factorizations of (2)w7.
• Index entries for linear recurrences with constant coefficients, signature (11,-10).

Programs

Mathematica

Table[FromDigits[PadLeft[{7},n,2]],{n,20}] (* or *) LinearRecurrence[{11,-10},{7,27},20] (* Harvey P. Dale, Jan 06 2023 *)

PARI

my(x='x+O('x^22)); Vec(x*(7-50*x)/((1-11*x+10*x^2))) \\ Elmo R. Oliveira, Jun 17 2025

Formula

a(n) = 10*a(n-1) - 43 with n>1, a(1)=7. - Vincenzo Librandi, Dec 05 2010

a(n) = a(n-1) + 2*10^(n-1) with n>1, a(1)=7. - Zak Seidov, Dec 05 2010

From Colin Barker, Jan 24 2013: (Start)

a(n) = 11*a(n-1) - 10*a(n-2).

G.f.: -x*(50*x-7)/((x-1)*(10*x-1)). (End)

E.g.f.: -5 + exp(x)*(43 + 2*exp(9*x))/9. - Elmo R. Oliveira, Jun 17 2025

Extensions

More terms from Vincenzo Librandi, Feb 24 2010

a(19)-a(21) from Elmo R. Oliveira, Jun 17 2025