A138720 Concatenation of k digits 1, k digits 0 and k digits 1, where k is the n-th positive triangular number.

101, 111000111, 111111000000111111, 111111111100000000001111111111, 111111111111111000000000000000111111111111111, 111111111111111111111000000000000000000000111111111111111111111

Offset: 1

Author

Omar E. Pol, Mar 29 2008

Keywords

• base
• easy
• nonn

Crossrefs

Cf. A000217, 138711, A138179, A138721, A138722.

Programs

Mathematica

Table[c=(n(n+1))/2;FromDigits[Join[PadRight[{},c,1],PadRight[{},c,0], PadRight[{},c,1]]],{n,10}] (* Harvey P. Dale, Oct 15 2013 *)