A186194 A002275(n) * (A002275(n)+1).

0, 2, 132, 12432, 1235432, 123465432, 12345765432, 1234568765432, 123456798765432, 12345679098765432, 1234567902098765432, 123456790132098765432, 12345679012432098765432, 1234567901235432098765432, 123456790123465432098765432

Offset

0,2

Comments

a(1),a(2),a(3),a(4),a(5) are (between the two 0's) the cores of the decimal expansions of a(10),a(11),a(12),a(13),a(14).

First differences begin 130,12300,1223000,122230000,....

Links

Table of n, a(n) for n=0..14.

Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).

Formula

a(n)=2*A003555(n+1).

n 1's followed by n 8's is b(n)=18,1188,111888,11118888,1111188888, ...; then a(n)=b(n)/9. See its "contrary" A184337(n+1).

G.f. 2*x*(-1+45*x) / ( (x-1)*(100*x-1)*(10*x-1) ). - R. J. Mathar, Mar 10 2011

Example

a(1)=1*2=2, a(2)=11*12=132, a(3)=111*112=12432.

Mathematica

LinearRecurrence[{111, -1110, 1000}, {0, 2, 132}, 20] (* Harvey P. Dale, Apr 08 2022 *)

Crossrefs

Sequence in context: A020524 A157071 A174585 * A099682 A214436 A135759

Adjacent sequences: A186191 A186192 A186193 * A186195 A186196 A186197

Keyword

nonn,easy

Author

Paul Curtz, Feb 14 2011

Extensions

Zero added by Franklin T. Adams-Watters, Mar 09 2011

Status

approved