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%I #16 Sep 08 2022 08:45:14
%S 81,1620,24300,324000,4050000,48600000,567000000,6480000000,
%T 72900000000,810000000000,8910000000000,97200000000000,
%U 1053000000000000,11340000000000000,121500000000000000,1296000000000000000
%N Number of combinations of two natural numbers that together have n digits.
%H Vincenzo Librandi, <a href="/A096302/b096302.txt">Table of n, a(n) for n = 2..100</a>
%F a(n) = Sum_{i=0..n-1} binomial(n-1, i)*9^(i+1)*i.
%F a(n) = 81*(n-1)*10^(n-2). - _Vladeta Jovovic_, Jun 26 2004
%t f[n_] := Sum[Binomial[n - 1, i]*9^(i + 1)*i, {i, 0, n}]; Table[ a[n], {n, 2, 17}] (* _Robert G. Wilson v_, Jun 30 2004 *)
%o (Magma) [81*(n-1)*10^(n-2): n in [2..30]]; // _Vincenzo Librandi_, Jun 06 2011
%Y Cf. A053541.
%K nonn,easy,base
%O 2,1
%A Hagai Helman (Helman(AT)actcom.net.il), Jun 25 2004
%E More terms from _Robert G. Wilson v_, Jun 30 2004
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