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A181597 (N\{4})-perfect numbers, i.e., numbers m for which sigma(m)-4 = 2m, if 4|m, otherwise sigma(m) = 2m. 2
6, 12, 88, 1888, 32128, 521728, 1848964, 8378368, 34359083008, 549753192448 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Or union of {6}, near-perfect numbers m (cf. A181595) for which d(m)=4, and all odd perfect numbers (if they exist). Note that (N\{2})-perfect numbers are numbers for which sigma(m)-2=2m, if m is even, and sigma(m)=2m, if m is odd. They are all even numbers of A045768 and all odd perfect numbers (if they exist).

LINKS

Table of n, a(n) for n=1..10.

EXAMPLE

88 is in the sequence since sigma(88) = 180 and 180 - 4 = 2*88.

CROSSREFS

Cf. A000396, A005101, A005820, A088832, A118372, A153501, A181595, A181596.

Sequence in context: A054883 A005402 A128953 * A002898 A003613 A099767

Adjacent sequences:  A181594 A181595 A181596 * A181598 A181599 A181600

KEYWORD

nonn,more

AUTHOR

Vladimir Shevelev, Nov 01 2010, Nov 03 2010

EXTENSIONS

Invalid term removed and a(8)-a(10) from Donovan Johnson, Sep 14 2013

STATUS

approved

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Last modified May 28 16:37 EDT 2022. Contains 354119 sequences. (Running on oeis4.)