login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A113546 Let S(n)=1/3*sigma(n). Numbers such that S(S(n))=n, 1/3-sociable number of order 1 or 2. 1
120, 672, 7680, 8184, 523776, 1100190, 1124352, 14913024, 16149760, 459818240, 775898880, 874897408, 1476304896, 51001180160 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(1), a(2), a(5) and a(10) are 3-perfect numbers (A005820).

a(4) = S(a(3)).

a(15) > 1.5*10^11. - Giovanni Resta, Jul 21 2015

LINKS

Table of n, a(n) for n=1..14.

Eric Weisstein's World of Mathematics, Sociable Numbers

PROG

(PARI) isok(n) = (type(s=sigma(n)/3) == "t_INT") && (sigma(s)/3 == n); \\ Michel Marcus, Feb 20 2014

CROSSREFS

Cf. A113286.

Sequence in context: A229568 A292365 A306373 * A281771 A166069 A114887

Adjacent sequences:  A113543 A113544 A113545 * A113547 A113548 A113549

KEYWORD

nonn,more

AUTHOR

Yasutoshi Kohmoto, Jan 27 2006

EXTENSIONS

a(6)-a(9) from Michel Marcus, Feb 20 2014

a(10)-a(12) from Michel Marcus, Feb 24 2014

Typo corrected by Mauro Fiorentini, Jul 21 2015

a(13)-a(14) from Giovanni Resta, Jul 22 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 26 01:48 EST 2020. Contains 331270 sequences. (Running on oeis4.)