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A067680 Numbers k such that sigma(2k + 2) = 4k. 1
6, 21, 54, 75, 441, 1071, 4191, 9315, 58311, 4197375, 7685151, 36997695, 268460031, 1073790975, 17180065791, 13517087570210304, 18014398710808575, 288230376957018111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If k is a term, then 2*k + 2 is a term of A125246. - Jinyuan Wang, Apr 08 2020

LINKS

Table of n, a(n) for n=1..18.

PROG

(PARI) isok(k) = sigma(2*k+2) == 4*k; \\ Michel Marcus, Apr 06 2020

CROSSREFS

Cf. A000203, A125246.

Sequence in context: A135454 A069778 A015644 * A115052 A025203 A262719

Adjacent sequences:  A067677 A067678 A067679 * A067681 A067682 A067683

KEYWORD

nonn,more

AUTHOR

Benoit Cloitre, Feb 04 2002

EXTENSIONS

a(9) from Benoit Cloitre and Neven Juric (neven.juric(AT)apis-it.hr), May 21 2004

a(10)-a(15) from Donovan Johnson, Jan 31 2009

a(16)-a(18) from Jinyuan Wang, Apr 06 2020

STATUS

approved

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Last modified July 26 01:49 EDT 2021. Contains 346294 sequences. (Running on oeis4.)