OFFSET
0,2
COMMENTS
An Iraqi tablet dating from the Middle Babylonian period (1400-1100 BC) gives a(1)-a(20), a(30), a(40), and a(50). See CDLI link for images and more information. - Charles R Greathouse IV, Jan 21 2017
Apart from 0, numbers whose digital root is 9. - Halfdan Skjerning, Mar 15 2018
LINKS
Ivan Panchenko, Table of n, a(n) for n = 0..200
CDLI, MKT 1, 039, HS 0217a
Tanya Khovanova, Recursive Sequences
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 321
Luis Manuel Rivera, Integer sequences and k-commuting permutations, arXiv preprint arXiv:1406.3081 [math.CO], 2014-2015.
Leo Tavares, Illustration: Triangular Frames
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
From Vincenzo Librandi, Dec 24 2010: (Start)
a(n) = 9*n = 2*a(n-1) - a(n-2).
G.f.: 9x/(x-1)^2. (End)
E.g.f.: 9*x*exp(x). - Stefano Spezia, Oct 08 2022
MATHEMATICA
Range[0, 1000, 9] (* Vladimir Joseph Stephan Orlovsky, May 27 2011 *)
PROG
(PARI) a(n)=9*n \\ Charles R Greathouse IV, Jan 30 2012
(Maxima) makelist(9*n, n, 0, 20); /* Martin Ettl, Dec 17 2012 */
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved