OFFSET
1,2
COMMENTS
Digital sum of a(n) = digsum(n) + 1 for n>1.
3, 229, 4987 are the initial values of n for prime a(n). - Altug Alkan, Jan 17 2016
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (12,-21,10).
FORMULA
a(n) = n + 10^(n-1) for n>1 with a(1) = 1.
a(n) = A081552(n) - 1 for n>1. - Michel Marcus, Jan 10 2016
From Colin Barker, Jan 10 2016: (Start)
a(n) = 12*a(n-1) - 21*a(n-2) + 10*a(n-3) for n>3.
G.f.: x*(1-20*x^2+10*x^3) / ((1-x)^2*(1-10*x)). (End)
EXAMPLE
a(4) = 1004 because it is the smallest 4-digit number ending in 4.
MATHEMATICA
Join[{1}, Table[n + 10^(n - 1), {n, 2, 20}]]
PROG
(Magma) [1] cat [n+10^(n-1): n in [2..30]]; // Vincenzo Librandi, Jan 10 2016
(PARI) Vec(x*(1-20*x^2+10*x^3)/((1-x)^2*(1-10*x)) + O(x^30)) \\ Colin Barker, Jan 10 2016
(PARI) a(n) = if(n==1, 1, n + 10^(n-1)); \\ Altug Alkan, Jan 17 2016
(Python)
def A266959(n): return n+10**(n-1) if n > 1 else 1 # Chai Wah Wu, Jul 25 2022
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Wesley Ivan Hurt, Jan 09 2016
STATUS
approved