%I #6 Jul 22 2014 22:18:10
%S 7,14,28,70,161,378,882,2058,4802,11200,26138,60984,142296,332024,
%T 774725,1807694,4217948,9841881,22964389,53583572,125028337,291732784,
%U 680709834,1588322946,3706086874,8647536037,20177584084,47081029534,109855735577,256330049682
%N Number of nonnegative integers with property that their base 7/3 expansion (see A024640) has n digits.
%e The only integers requiring two digits in base 7/3 are 30, 31, 32, 33, 34, 35, 36, 60, 61, 62, 63, 64, 65, 66, representing 7-20 respectively; thus, a(2) = 14.
%o (Sage)
%o A=[1]
%o for i in [1..100]:
%o A.append(ceil(((7-3)/3)*sum(A)))
%o [7*x for x in A]
%Y Cf. A245356, A081848, A024640.
%K nonn,base
%O 1,1
%A _Tom Edgar_, Jul 21 2014