A111177 - OEIS

%I #8 Oct 31 2013 12:17:31

%S 4,21,130,913,7176,62629,602806,6356865,72994348,907497301,

%T 12152572554,174476220241,2674434002800,43603430324133,

%U 753581024080126,13763517571878529,264919276238885076,5360264479811601685

%N Number of base n numbers in which each digit appears at most once (all unnecessary 0's deleted).

%C Finite expansions after the "decimal" point are allowed, but there must be a number before it (so we can have 0.1, but not .01).

%H Cf. A001339.

%F a(n)=Sum(i=0, n-1) (i^2+i+1)(n-1)!/(n-1-i)!; n>1

%e a(2)=4 because in the binary system only the numbers 0; 1; 0.1; 10 can be written with each digit used at most once (all unnecessary 0's deleted).

%t f[n_] := Sum[(i^2 + i + 1)(n - 1)!/(n - 1 - i)!, {i, 0, n - 1}]; Table[ f[n], {n, 2, 19}] (* _Robert G. Wilson v_ *)

%K nonn,base

%O 2,1

%A Rafael Hofman (mathematics287(AT)yahoo.de), Oct 22 2005

%E More terms from _Robert G. Wilson v_, Oct 29 2005