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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. 4
 101, 111000111, 111111000000111111, 111111111100000000001111111111, 111111111111111000000000000000111111111111111, 111111111111111111111000000000000000000000111111111111111111111 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified September 8 15:42 EDT 2024. Contains 375753 sequences. (Running on oeis4.)