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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
OFFSET
1,1
COMMENTS
If k is a term, then 2*k + 2 is a term of A125246. - Jinyuan Wang, Apr 08 2020
PROG
(PARI) isok(k) = sigma(2*k+2) == 4*k; \\ Michel Marcus, Apr 06 2020
CROSSREFS
Sequence in context: A135454 A069778 A015644 * A115052 A025203 A262719
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