A253515 Count down from 2*k to 1, then from 2*(k+1) to 1 and so on.

2, 1, 4, 3, 2, 1, 6, 5, 4, 3, 2, 1, 8, 7, 6, 5, 4, 3, 2, 1, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1

Offset: 1

Author

Mikael Aaltonen, Jan 03 2015

Keywords

• nonn

Crossrefs

Cf. A074294.

Programs

Mathematica

a253515[n_] := Block[{f}, f[x_] := 1 - x + Floor[Sqrt[x] + 3/2] * Floor[Sqrt[x] + 1/2]; Array[f, n]]; a253515[100] (* Michael De Vlieger, Jan 03 2015 *)
Flatten[Table[Range[2n,1,-1],{n,10}]] (* Harvey P. Dale, Jan 15 2016 *)

Formula

a(n) = 1 - n + floor(sqrt(n)+3/2)*floor(sqrt(n)+1/2).

a(n) = A130829(n) - A074294(n).