A074993 a(n) = floor((concatenation of n, n+1)/2).

0, 6, 11, 17, 22, 28, 33, 39, 44, 455, 505, 556, 606, 657, 707, 758, 808, 859, 909, 960, 1010, 1061, 1111, 1162, 1212, 1263, 1313, 1364, 1414, 1465, 1515, 1566, 1616, 1667, 1717, 1768, 1818, 1869, 1919, 1970, 2020, 2071, 2121, 2172, 2222, 2273, 2323, 2374

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.

Links

Table of n, a(n) for n=0..47.

Mathematica

cc[n_]:=Floor[FromDigits[Join[IntegerDigits[n], IntegerDigits[n+1]]]/2]; Array[cc, 40, 0] (* Harvey P. Dale, Nov 11 2011 *)

Crossrefs

Cf. A001704, A074991, A074992, A074994, A074995, A074996, A074997, A073086, A074999, A127421.

Sequence in context: A315522 A315523 A315524 * A315525 A231001 A315526

Adjacent sequences: A074990 A074991 A074992 * A074994 A074995 A074996

Keyword

base,easy,nonn

Author

Amarnath Murthy, Aug 31 2002

Status

approved