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 A273751 Triangle of the natural numbers written by decreasing antidiagonals. 2
 1, 2, 3, 4, 5, 7, 6, 8, 10, 13, 9, 11, 14, 17, 21, 12, 15, 18, 22, 26, 31, 16, 19, 23, 27, 32, 37, 43, 20, 24, 28, 33, 38, 44, 50, 57, 25, 29, 34, 39, 45, 51, 58, 65, 73, 30, 35, 40, 46, 52, 59, 66, 74, 82, 91, 36, 41 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A permutation of the natural numbers. a(n) and A091995(n) are different at the ninth term. Antidiagonal sums: 1, 2, 7, 11, ... = A235355(n+1). Same idea. Row sums: 1, 5, 16, 37, 72, 124, 197, 294, ... = 7*n^3/12 -n^2/8 +5*n/12 +1/16 -1/16*(-1)^n with g.f. x*(1+2*x+3*x^2+x^3) / ( (1+x)*(x-1)^4 ). The third difference is of period 2: repeat [3, 4]. Indicates the order in which electrons fill the different atomic orbitals (s,p,d,f,g,h). - Alexander Goebel, May 12 2020 LINKS Wikipedia, Atomic orbital EXAMPLE 1, 2,   3, 4,   5,  7, 6,   8, 10, 13, 9,  11, 14, 17, 21, 12, 15, 18, 22, 26, 31, 16, 19, 23, 27, 32, 37, 43, 20, etc. MAPLE A273751 := proc(n, k)     option remember;     if k = n then         A002061(n) ;     elif k > n or k < 0 then         0;     elif k = n-1 then         procname(n-1, k)+k ;     else         procname(n-1, k+1)+1 ;     end if; end proc: # R. J. Mathar, Jun 13 2016 MATHEMATICA T[n_, k_] := T[n, k] = Which[k == n, n(n-1) + 1, k == n-1, (n-1)^2 + 1, k == 1, n + T[n-2, 1], 1 < k < n-1, T[n-1, k+1] + 1, True, 0]; Table[T[n, k], {n, 12}, {k, n}] // Flatten (* Jean-François Alcover, Jun 10 2016 *) CROSSREFS Cf. A002061 (right diagonal), A002620 (first column), A033638, A091995, A234305 (antidiagonals of the triangle). Sequence in context: A247714 A283734 A293052 * A056017 A091995 A343150 Adjacent sequences:  A273748 A273749 A273750 * A273752 A273753 A273754 KEYWORD nonn AUTHOR Paul Curtz, May 30 2016 STATUS approved

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Last modified June 24 02:56 EDT 2021. Contains 345415 sequences. (Running on oeis4.)