A173772 a(n) = (4*10^n + 23)/9.

7, 47, 447, 4447, 44447, 444447, 4444447, 44444447, 444444447, 4444444447, 44444444447, 444444444447, 4444444444447, 44444444444447, 444444444444447, 4444444444444447, 44444444444444447, 444444444444444447, 4444444444444444447, 44444444444444444447, 444444444444444444447

Offset: 1

Author

Vincenzo Librandi, Feb 24 2010

Keywords

• nonn
• easy

Links

• Index entries for linear recurrences with constant coefficients, signature (11,-10).

Crossrefs

Cf. A173771 (primes).

Programs

Mathematica

LinearRecurrence[{11,-10},{7,47},30] (* or *) Table[FromDigits[ PadLeft[ {7},n,4]],{n,30}] (* Harvey P. Dale, Dec 27 2014 *)

PARI

a(n)=4*10^n\9+3 \\ Charles R Greathouse IV, Jan 11 2012

Formula

a(n) = 10*a(n-1) - 23 with n > 1, a(1) = 7.

a(n) = 11*a(n-1) - 10*a(n-2). G.f.: -x*(30*x-7)/((x-1)*(10*x-1)). [Colin Barker, Jan 24 2013]

E.g.f.: exp(x)*(4*exp(9*x) + 23)/9. - Elmo R. Oliveira, Sep 09 2024

Extensions

a(19)-a(21) from Elmo R. Oliveira, Sep 09 2024