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A128823 a(n) is the sum of all n-digit Fibonacci numbers.

%I A128823 #29 Jun 29 2019 02:19:41
%S A128823 20,212,2351,15127,178707,1981891,21979508,141422324,1670731762,
%T A128823 18528699171,205486422643,2278879348244,14662949395604,
%U A128823 173224810531570,1921092587268915,21305243270489635,236278768562654900
%N A128823 a(n) is the sum of all n-digit Fibonacci numbers.
%C A128823 The minimum, average and maximum of a(n)/10^n are approximately equal to 1.38197968245, 1.87028385088 & 2.38195747810, respectively, for the first 30000 terms.
%C A128823 Observation: the minimum seems to be just over (5-sqrt(5))/2, the maximum seems to be just shy of (7-sqrt(5))/2; the average is not (6-sqrt(5))/2 but seems to be closer to (5-sqrt(11))/9. - _Robert G. Wilson v_, May 26 2007
%C A128823 Observation: There are approximately twice as many odd terms as even ones.
%H A128823 Robert G. Wilson v, <a href="/A128823/b128823.txt">Table of n, a(n) for n = 1..100</a>
%H A128823 C. Valente, PlanetMath.org, <a href="http://planetmath.org/listoffibonaccinumbers">List of Fibonacci Numbers</a>
%H A128823 Wikipedia, <a href="http://en.wikipedia.org/wiki/Fibonacci_number">Fibonacci Numbers</a>.
%F A128823 a(n) = A000045(A072354(n+1)+1) - A000045(A072354(n)+1). - _Christopher Hohl_, May 27 2019
%e A128823 If n=1 then the sum of the Fibonacci numbers 1+1+2+3+5+8 = 20 which is the first term in the sequence.
%e A128823 If n=2 then the sum of the Fibonacci numbers 13+21+34+55+89 = 212 which is the second term in the sequence.
%t A128823 f[n_] := Plus @@ Select[ Fibonacci /@ Range[ Floor[(n - 1)*Log[ GoldenRatio, 10] + 1], Floor[ n*Log[ GoldenRatio, 10] + 3]], Floor@ Log[10, # ] + 1 == n &]; Array[f, 18] (* _Robert G. Wilson v_, May 26 2007 *)
%Y A128823 Cf. A000045, A072354.
%K A128823 nonn,base
%O A128823 1,1
%A A128823 _Parthasarathy Nambi_, Apr 11 2007
%E A128823 More terms from _Robert G. Wilson v_, May 26 2007