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a(n) = (1/9)*(-1+10^n)*(4*n+3)
0

%I #4 Oct 03 2013 09:31:24

%S 7,121,1665,21109,255553,2999997,34444441,388888885,4333333329,

%T 47777777773,522222222217,5666666666661,61111111111105,

%U 655555555555549,6999999999999993,74444444444444437,788888888888888881

%N a(n) = (1/9)*(-1+10^n)*(4*n+3)

%C Numbers with increasingly larger and larger one-digit centers.

%D Discovered by Jason Earls.

%F O.g.f.: -x*(2*x+7)*(5*x-1)/[(-1+x)^2*(-1+10*x)^2]. - _R. J. Mathar_, Feb 26 2008

%K easy,nonn

%O 1,1

%A _Michael Joseph Halm_, Jul 10 2004