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A319902 Unitary sociable numbers of order 4. 5
263820, 263940, 280380, 280500, 395730, 395910, 420570, 420750, 172459210, 209524210, 218628662, 218725430, 230143790, 231439570, 246667790, 272130250, 384121920, 384296640, 408233280, 408408000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Is this a duplicate of A098188? - R. J. Mathar, Oct 04 2018

Note that the first 4 terms and the next 4 terms form two sociable groups. But then the 8 next terms belong to two distinct sociable groups. Whereas in A098188, the integers are grouped by cycle.

LINKS

Table of n, a(n) for n=1..20.

J. O. M. Pedersen, Known Unitary Sociable Numbers of order four [Via Internet Archive Wayback-Machine]

J. O. M. Pedersen, Order 4 cycles, 2007.

Eric Weisstein's World of Mathematics, Unitary Sociable Numbers

PROG

(PARI) f(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d)) - n;

isok4(n) = iferr(f(f(f(f(n)))) == n, E, 0);

isok2(n) = iferr(f(f(n)) == n, E, 0);

isok1(n) = iferr(f(n) == n, E, 0);

isok(n) = isok4(n) && !isok1(n) && !isok2(n);

CROSSREFS

Cf. A063919 (sum of proper unitary divisors).

Cf. A002827 (unitary perfect), A063991 (unitary amicable).

Cf. A097024 (order 5), A097030 (order 14).

Cf. A090615 (least member of sociable quadruples).

Sequence in context: A253933 A237778 A123138 * A098188 A095974 A022202

Adjacent sequences:  A319899 A319900 A319901 * A319903 A319904 A319905

KEYWORD

nonn,more

AUTHOR

Michel Marcus, Oct 01 2018

STATUS

approved

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Last modified April 19 10:38 EDT 2019. Contains 322253 sequences. (Running on oeis4.)