cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A102543 Antidiagonal sums of the antidiagonals of Losanitsch's triangle.

Original entry on oeis.org

1, 1, 1, 2, 2, 3, 4, 6, 8, 12, 16, 24, 33, 49, 69, 102, 145, 214, 307, 452, 653, 960, 1393, 2046, 2978, 4371, 6376, 9354, 13665, 20041, 29307, 42972, 62884, 92191, 134974, 197858, 289772, 424746, 622198, 911970, 1336121, 1958319, 2869417, 4205538, 6162579, 9031996, 13235661, 19398240
Offset: 0

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Author

Gerald McGarvey, Feb 24 2005

Keywords

Comments

The Ca1 and Ca2 sums, see A180662 for their definitions, of Losanitsch's triangle A034851 equal this sequence. - Johannes W. Meijer, Jul 14 2011
For n >= 5, a(n+1)-1 is the number of non-isomorphic snake polyominoes with n cells that can be inscribed in a rectangle of height 2. - Christian Barrientos and Sarah Minion, Jul 29 2018

Crossrefs

Programs

  • Maple
    A102543 := proc(n): (A000930(n)+x(n)+x(n-1)+x(n-3))/2 end: A000930:=proc(n): sum(binomial(n-2*i, i), i=0..n/3) end: x:=proc(n): if type(n, even) then A000930(n/2) else 0 fi: end: seq(A102543(n), n=0..38); # Johannes W. Meijer, Jul 14 2011
  • Mathematica
    CoefficientList[Series[(1 - x^2 - x^4 - x^6)/((x^3 + x - 1)*(x^6 + x^2 - 1)), {x, 0, 50}], x] (* G. C. Greubel, Apr 27 2017 *)
    LinearRecurrence[{1,1,0,0,-1,1,-1,0,-1},{1,1,1,2,2,3,4,6,8},50] (* Harvey P. Dale, Dec 14 2023 *)
  • PARI
    x='x+O('x^50); Vec((1 - x^2 - x^4 - x^6)/((x^3 + x - 1)*(x^6 + x^2 - 1))) \\ G. C. Greubel, Apr 27 2017

Formula

a(n) = A068927(n-1), n>3.
From Johannes W. Meijer, Jul 14 2011: (Start)
G.f.: (-1/2)*(1/(x^3+x-1)+(1+x+x^3)/(x^6+x^2-1))= ( 1-x^2-x^4-x^6 ) / ( (x^3+x-1)*(x^6+x^2-1) ).
a(n) = (A000930(n)+x(n)+x(n-1)+x(n-3))/2 with x(2*n) = A000930(n) and x(2*n+1) = 0. (End)

A100806 a(1) = 1; for n>=2, a(n) = A001221(n)-th positive integer not yet in the sequence.

Original entry on oeis.org

1, 2, 3, 4, 5, 7, 6, 8, 9, 11, 10, 13, 12, 15, 16, 14, 17, 19, 18, 21, 22, 23, 20, 25, 24, 27, 26, 29, 28, 32, 30, 31, 34, 35, 36, 37, 33, 39, 40, 41, 38, 44, 42, 45, 46, 47, 43, 49, 48, 51, 52, 53, 50, 55, 56, 57, 58, 59, 54, 62, 60, 63, 64, 61, 66, 68, 65, 69, 70, 72, 67, 73
Offset: 1

Views

Author

Leroy Quet, Jan 04 2005

Keywords

Comments

A permutation of the positive integers.

Crossrefs

Inverse: A102451; A102450(n) = a(a(n)).
Cf. A102452.

Programs

  • Mathematica
    Block[{a = {1}, nn = 72, s, P = FoldList[Times, Prime@ Range@ 12]}, s = Range[2, nn + LengthWhile[P, # <= nn &]]; Do[AppendTo[a, s[[PrimeNu@ i ]]]; s = Complement[s, a], {i, 2, nn}]; a] (* Michael De Vlieger, Sep 24 2017 *)

Extensions

More terms from Reinhard Zumkeller, Jan 09 2005
Showing 1-2 of 2 results.