A326063 - OEIS

A326063

Composite numbers n such that (A001065(n) - A032742(n)) divides (n - A032742(n)), where A032742 gives the largest proper divisor, and A001065 is the sum of proper divisors.

4, 6, 9, 25, 28, 49, 117, 121, 169, 289, 361, 496, 529, 775, 841, 961, 1369, 1681, 1849, 2209, 2809, 3481, 3721, 4489, 5041, 5329, 6241, 6889, 7921, 8128, 9409, 10201, 10309, 10609, 11449, 11881, 12769, 16129, 17161, 18769, 19321, 22201, 22801, 24649, 26569, 27889, 29929, 32041, 32761, 36481, 37249, 38809, 39601, 44521, 49729, 51529, 52441

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OFFSET

1,1

COMMENTS

Composite numbers n such that A318505(n) [sum of divisors of n excluding n itself and the second largest of them, A032742(n)] divides A060681(n) [the largest difference between consecutive divisors of n, = n - A032742(n)].

Numbers k such that A326062(k) = A318505(k).

Question: Is it possible that this sequence could contain a term with more than one non-unitary prime factor? If not, then there are no odd perfect numbers. (See e.g., A326137).

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..1001

Index entries for sequences where any odd perfect numbers must occur

Index entries for sequences related to sigma(n)

EXAMPLE

For n = 9 = 3*3, its divisors are [1, 3, 9], thus A318505(9) = 1 and A060681(9) = 9-3 = 6, and 1 divides 6, so 9 is included, like all squares of primes.

For n = 117 = 3^2 * 13,its divisors are [1, 3, 9, 13, 39, 117], thus A318505(117) = 1+3+9+13 = 26 and A060681(117) = (117-39) = 78, which is a multiple of 26, thus 117 is included in the sequence.

PROG

(PARI)

A032742(n) = if(1==n, n, n/vecmin(factor(n)[, 1]));

isA326063(n) = (gcd((sigma(n)-A032742(n))-n, n-A032742(n)) == (sigma(n)-A032742(n))-n);

(PARI)

A060681(n) = (n-A032742(n));

A318505(n) = if(1==n, 0, (sigma(n)-A032742(n))-n);

isA326063(n) = { my(t=A318505(n)); (t && !(A060681(n)%t)); };

CROSSREFS

Cf. A000203, A001065, A032742, A060681, A318505, A325981, A326062, A326137.

Subsequences: A000396, A001248, A326064 (odd terms that are not squares of primes).

Sequence in context: A338309 A246569 A368648 * A085721 A190300 A338378

Adjacent sequences: A326060 A326061 A326062 * A326064 A326065 A326066

KEYWORD

nonn

AUTHOR

Antti Karttunen, Jun 06 2019

STATUS

approved