A138720 - OEIS

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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

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..6.

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 *)

CROSSREFS

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

Sequence in context: A262645 A138826 A292686 * A262627 A259199 A006064

Adjacent sequences: A138717 A138718 A138719 * A138721 A138722 A138723

KEYWORD

base,easy,nonn

AUTHOR

Omar E. Pol, Mar 29 2008

STATUS

approved