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A097024 Numbers in the 5-cycle-attractor if the function f(x)=A063919(x) is iterated; f(x) is the sum of unitary proper divisors. 23
1482, 1878, 1890, 2142, 2178 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A002827 provides 1-cycle terms = unitary perfect numbers.

A063991 gives 2-cycle elements = unitary amicable numbers.

A097030 collects true 14-cycle elements, i.e., terms in end-cycle of length 14 when A063919(x) function is iterated.

Concerning 3-cycle elements, only {30,42,54} were encountered.

LINKS

Table of n, a(n) for n=1..5.

J. O. M. Pedersen, Order 5 cycles, 2007.

PROG

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

isok5(n) = iferr(f(f(f(f(f(n))))) == n, E, 0);

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

isok(n) = !isok1(n) && isok5(n); \\ Michel Marcus, Sep 28 2018

CROSSREFS

Cf. A063919, A002827, A063991, A097030.

Sequence in context: A255789 A159719 A052167 * A253331 A158770 A252366

Adjacent sequences:  A097021 A097022 A097023 * A097025 A097026 A097027

KEYWORD

nonn,more

AUTHOR

Labos Elemer, Aug 30 2004

STATUS

approved

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Last modified December 9 17:18 EST 2019. Contains 329879 sequences. (Running on oeis4.)