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A066240 The floor(n/2)-perfect numbers, where f-perfect numbers for an arithmetical function f are defined in A066218. 0
18, 20, 70, 104, 464, 1952 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..6.

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

Sequence in context: A075865 A250113 A182226 * A115747 A185099 A216295

Adjacent sequences:  A066237 A066238 A066239 * A066241 A066242 A066243

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Dec 19 2001

STATUS

approved

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Last modified February 20 22:25 EST 2018. Contains 299387 sequences. (Running on oeis4.)