A179557 a(1)=10; a(n)=a(n-1)*10 -/+ 1 (alternating)

10, 99, 991, 9909, 99091, 990909, 9909091, 99090909, 990909091, 9909090909, 99090909091, 990909090909, 9909090909091, 99090909090909, 990909090909091, 9909090909090909, 99090909090909091, 990909090909090909, 9909090909090909091, 99090909090909090909

Offset

1,1

Comments

109/110 = 0,9909090909....

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..100

Index entries for linear recurrences with constant coefficients, signature (9, 10).

Formula

a(1)=10, a(2)=99, a(n)=9*a(n-1)+10*a(n-2). - Harvey P. Dale, Jul 21 2014

Mathematica

nxt[{a_, i_}]:={10a+i, -i}; Transpose[NestList[nxt, {10, -1}, 30]][[1]] (* or *) LinearRecurrence[{9, 10}, {10, 99}, 30] (* Harvey P. Dale, Jul 21 2014 *)

Prog

(Magma) [(1/11)*((-1)^(n-1)+109*10^(n-1)): n in [1..20]]; // Vincenzo Librandi, Jul 21 2014

Crossrefs

Sequence in context: A179477 A179555 A105694 * A300000 A213454 A000456

Adjacent sequences: A179554 A179555 A179556 * A179558 A179559 A179560

Keyword

nonn,easy

Author

Mark Dols, Jul 19 2010

Status

approved