OFFSET
1,2
COMMENTS
A k-digit number is in the sequence with probability ~ 1/sqrt(2*Pi*k/5). - Charles R Greathouse IV, Feb 19 2014
The number of d-digits positive terms is given by 7*8^(d-1)+ 7*sum(k=1,..,floor((d-1)/2), 8^(d-1-2*k) (k, k, d-1-2*k)!) + 2*sum(k=1,..,floor(d/2), 8^(d-2*k) (k, k-1, d-2*k)!), where (x,y,z)! = (x+y+z)!/(x! y! z!) denotes a multinomial coefficient. (* Giovanni Resta, Feb 22 2014 *)
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1500
MATHEMATICA
Select[Range[0, 200], DigitCount[#, 10, 1]==DigitCount[#, 10, 9]&] (* Harvey P. Dale, Feb 19 2014 *)
PROG
(PARI) is(n)=my(v=digits(n)); sum(i=1, #v, if(v[i]==1, 1, if(v[i]==9, -1, 0)))==0 \\ Charles R Greathouse IV, Feb 19 2014
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
STATUS
approved