A086520 - OEIS

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A086520

Number of integers strictly greater than (n-sqrt(n))/2 and strictly less than (n+sqrt(n))/2.

0, 0, 1, 2, 1, 2, 3, 2, 3, 2, 3, 4, 3, 4, 3, 4, 3, 4, 5, 4, 5, 4, 5, 4, 5, 4, 5, 6, 5, 6, 5, 6, 5, 6, 5, 6, 5, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 6, 7, 8, 7, 8, 7, 8, 7, 8, 7, 8, 7, 8, 7, 8, 7, 8, 9, 8, 9, 8, 9, 8, 9, 8, 9, 8, 9, 8, 9, 8, 9, 8, 9, 10, 9, 10, 9, 10, 9, 10, 9, 10, 9, 10, 9, 10, 9, 10, 9, 10, 9, 10

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,4

COMMENTS

This sequence occurs in quantum mechanics, in the context of counting certain kinds of inseparable states in an n-qubit model.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..1000

J. S. Pratt, Universality in the entanglement structure of ferromagnets, Phys. Rev. Lett. 93, 237205 (2004)

J. S. Pratt, Comments on this sequence

EXAMPLE

a(16) = 3 because there are three integers between 6 and 10.

MAPLE

a:= n-> max(0, ceil((n+sqrt(n))/2)-1-floor((n-sqrt(n))/2)):

seq(a(n), n=0..120); # Alois P. Heinz, Apr 02 2014

MATHEMATICA

a[n_] := If[IntegerQ[Sqrt[n]], Sum[1, {m, Ceiling[(n - Sqrt[n])/2] + 1, Floor[(n + Sqrt[n])/2] - 1}], Sum[1, {m, Ceiling[(n - Sqrt[n])/2], Floor[(n + Sqrt[n])/2]}]]

CROSSREFS

Sequence in context: A283431 A258594 A364215 * A012265 A339765 A268835

Adjacent sequences: A086517 A086518 A086519 * A086521 A086522 A086523

KEYWORD

easy,nonn

AUTHOR

Jeff S. Pratt (jpratt(AT)pas.rochester.edu), Sep 10 2003

EXTENSIONS

a(0)-a(1) prepended by Alois P. Heinz, Apr 02 2014

STATUS

approved