A066240 The floor(n/2)-perfect numbers, where f-perfect numbers for an arithmetical function f are defined in A066218.

18, 20, 70, 104, 464, 1952, 45356, 91388, 130304, 254012, 388076, 437745, 522752, 8382464, 134193152

Offset

1,1

Links

Table of n, a(n) for n=1..15.

J. Pe, On a Generalization of Perfect Numbers, J. Rec. Math., 31(3) (2002-2003), 168-172.

Example

Let f(n) = floor(n/2). Then f(18) = 9 = 4+3+1+1+0 = f(9)+f(6)+f(3)+f(2)+f(1); so 18 is a term of the sequence.

Mathematica

f[x_] := Floor[x/2]; Select[ Range[ 1, 10^5], 2 * f[ # ] == Apply[ Plus, Map[ f, Divisors[ # ] ] ] & ]

Crossrefs

Cf. A066218.

Sequence in context: A075865 A250113 A182226 * A115747 A303686 A185099

Adjacent sequences: A066237 A066238 A066239 * A066241 A066242 A066243

Keyword

nonn,more

Author

Joseph L. Pe, Dec 19 2001

Extensions

a(7)-a(15) from Amiram Eldar, Sep 26 2019

Status

approved