login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A178630 a(n) = 18 * ((10^n - 1)/9)^2. 13
18, 2178, 221778, 22217778, 2222177778, 222221777778, 22222217777778, 2222222177777778, 222222221777777778, 22222222217777777778, 2222222222177777777778, 222222222221777777777778 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..12.

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

FORMULA

a(n) = 18*A002477(n) = A002283(n)*A002276(n).

a(n)=((A002276(n-1)*10+1)*10^(n-1)+A002281(n-1))*10+8.

G.f.: 18*x*(1 + 10*x)/((1 - x)*(1 - 10*x)*(1 - 100*x)). - Ilya Gutkovskiy, Feb 24 2017

EXAMPLE

n=1: ..................... 18 = 9 * 2;

n=2: ................... 2178 = 99 * 22;

n=3: ................. 221778 = 999 * 222;

n=4: ............... 22217778 = 9999 * 2222;

n=5: ............. 2222177778 = 99999 * 22222;

n=6: ........... 222221777778 = 999999 * 222222;

n=7: ......... 22222217777778 = 9999999 * 2222222;

n=8: ....... 2222222177777778 = 99999999 * 22222222;

n=9: ..... 222222221777777778 = 999999999 * 222222222.

PROG

(MAGMA) [18*((10^n - 1)/9)^2: n in [1..50]]; // Vincenzo Librandi, Dec 28 2010

(PARI) a(n)=18*(10^n\9)^2 \\ Charles R Greathouse IV, Aug 21 2011

CROSSREFS

Cf. A075412, A178631, A075415, A178632, A178633, A178634, A178635, A059988.

Sequence in context: A296614 A230818 A276017 * A136834 A279296 A299696

Adjacent sequences:  A178627 A178628 A178629 * A178631 A178632 A178633

KEYWORD

nonn,easy

AUTHOR

Reinhard Zumkeller, May 31 2010

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 21 18:11 EDT 2018. Contains 316427 sequences. (Running on oeis4.)