OFFSET
0,2
COMMENTS
The first differences follow a pattern. Odd-indexed terms and even-indexed terms form separate A.P.s with the same common difference for all n except n = 10^k -1. The corresponding common differences are the repunits = (10^(d+1)-1)/9 where d = the number of digits in n.
MATHEMATICA
cc[n_]:=Floor[FromDigits[Join[IntegerDigits[n], IntegerDigits[n+1]]]/2]; Array[cc, 40, 0] (* Harvey P. Dale, Nov 11 2011 *)
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Aug 31 2002
STATUS
approved