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 A271439 If n is a triangular number, a(n) = 0, otherwise a(n) = n - A002024(n) + 1 4
 0, 0, 1, 0, 2, 3, 0, 4, 5, 6, 0, 7, 8, 9, 10, 0, 11, 12, 13, 14, 15, 0, 16, 17, 18, 19, 20, 21, 0, 22, 23, 24, 25, 26, 27, 28, 0, 29, 30, 31, 32, 33, 34, 35, 36, 0, 37, 38, 39, 40, 41, 42, 43, 44, 45, 0, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 0, 56, 57, 58 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS a(n) gives the number above n when the natural numbers are represented as a square array, or 0 if n is in the top row. 1 3 6 10 2 5 9 4 8 7 LINKS Peter Kagey, Table of n, a(n) for n = 0..10000 EXAMPLE As a regular triangle, sequence begins: 0; 0, 1; 0, 2, 3; 0, 4, 5, 6; 0, 7, 8, 9, 10; ... MATHEMATICA Riffle[#, 0] &@ Map[# (# - 1)/2 + Range@ # &, Range[0, 11]] /. {} -> {0} // Flatten (* Michael De Vlieger, Apr 07 2016 *) CROSSREFS Cf. A000217 (right diagonal), A006003 (row sums). Sequence in context: A198787 A193331 A091246 * A133637 A258093 A286578 Adjacent sequences:  A271436 A271437 A271438 * A271440 A271441 A271442 KEYWORD nonn,tabl AUTHOR Peter Kagey, Apr 07 2016 STATUS approved

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Last modified June 4 17:14 EDT 2020. Contains 334828 sequences. (Running on oeis4.)