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

1,1

Links

Table of n, a(n) for n=1..110.

Formula

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

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

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 *)

Crossrefs

Cf. A074294.

Sequence in context: A175702 A303781 A216377 * A319521 A281589 A302436

Adjacent sequences: A253512 A253513 A253514 * A253516 A253517 A253518

Keyword

nonn

Author

Mikael Aaltonen, Jan 03 2015

Status

approved