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 A187881 Triangle read by rows: the n-th column consists of n n's followed by 0's. 0
 1, 0, 2, 0, 2, 3, 0, 0, 3, 4, 0, 0, 3, 4, 5, 0, 0, 0, 4, 5, 6, 0, 0, 0, 4, 5, 6, 7, 0, 0, 0, 0, 5, 6, 7, 8, 0, 0, 0, 0, 5, 6, 7, 8, 9, 0, 0, 0, 0, 0, 6, 7, 8, 9, 10, 0, 0, 0, 0, 0, 6, 7, 8, 9, 10, 11 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Row sums = A001318: (1, 2, 5, 7, 12,...) The triangle is a variant of Janet's periodic table: .......1 .......2 .....2,3 .....3,4 ...3,4,5 ...4,5,6 .4,5,6,7 .5,6,7,8 ... LINKS Boris Putievskiy, Transformations (of) Integer Sequences And Pairing Functions, 2012,  arXiv:1212.2732 [math.CO]. Wikipedia, Electron configuration FORMULA As an infinite lower triangular matrix, A * B, where A = A101688 and B = an infinite lower triangular matrix with (1, 2, 3,...) as the main diagonal and the rest zeros. From Boris Putievskiy, Jan 09 2013: (Start) a(n) = A101688(n)*A002260(n). a(n) = floor((2*A002260(n)+1)/(A003056(n)+3))*A002260(n). a(n) = floor((2*n-t*(t+1)+1)/(t+3))*(n-t*(t+1)/2), where t = floor((-1+sqrt(8*n-7))/2). (End) EXAMPLE First few rows of the triangle = 1 0, 2 0, 2, 3 0, 0, 3, 4 0, 0, 3, 4, 5 0, 0, 0, 4, 5, 6 0, 0, 0, 4, 5, 6, 7 ... CROSSREFS Cf. A001318, A101688. Sequence in context: A098489 A128064 A144217 * A344839 A344836 A323474 Adjacent sequences:  A187878 A187879 A187880 * A187882 A187883 A187884 KEYWORD nonn,easy,tabl AUTHOR Gary W. Adamson, Mar 14 2011 STATUS approved

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Last modified June 19 20:27 EDT 2021. Contains 345145 sequences. (Running on oeis4.)