OFFSET
1,1
REFERENCES
Walther Lietzmann, Lustiges und Merkwuerdiges von Zahlen und Formen, (F. Hirt, Breslau 1921-43), p. 149.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).
FORMULA
EXAMPLE
n=1: ..................... 72 = 9 * 8;
n=2: ................... 8712 = 99 * 88;
n=3: ................. 887112 = 999 * 888;
n=4: ............... 88871112 = 9999 * 8888;
n=5: ............. 8888711112 = 99999 * 88888;
n=6: ........... 888887111112 = 999999 * 888888;
n=7: ......... 88888871111112 = 9999999 * 8888888;
n=8: ....... 8888888711111112 = 99999999 * 88888888;
n=9: ..... 888888887111111112 = 999999999 * 888888888.
MATHEMATICA
72 (FromDigits/@Table[PadRight[{}, n, 1], {n, 40}])^2 (* Vincenzo Librandi, Mar 21 2014 *)
PROG
(Magma) [72*((10^n-1)/9)^2: n in [1..50]]; // Vincenzo Librandi, Dec 28 2010
(PARI) a(n)=72*(10^n\9)^2 \\ Charles R Greathouse IV, Jul 02 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Reinhard Zumkeller, May 31 2010
STATUS
approved