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A253515 Count down from 2*k to 1, then from 2*(k+1) to 1 and so on. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 17 03:42 EDT 2021. Contains 347478 sequences. (Running on oeis4.)