The On-Line Encyclopedia of Integer Sequences (OEIS)

A325654 revision #22

A325654

Numbers m with a divisor d satisfying sigma(d) = 2*m.

6, 28, 496, 8128, 60480, 65520, 4357080, 33550336, 47139840, 91065600, 285981696, 2758909440, 8589869056, 87722956800, 132867440640, 137438691328, 306007080960, 806062473216, 1409150457792, 363485766938112, 12177456042320640, 29884246553283840

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OFFSET

1,1

COMMENTS

Even perfect numbers from A000396 are terms.

Numbers of the form A007691(k)*A054030(k)/2 when A054030(k) is even.

Subsequence of A323652.

Numbers of the form sigma(A325637(k))/2. - Jinyuan Wang, Jun 09 2019

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 1..1000

EXAMPLE

60480 is a term because 30240 divides 60480 and sigma(30240) = 120960 = 2*60480.

PROG

(Magma) [n: n in [1..100000] | #[d: d in Divisors(n) | SumOfDivisors(d) eq 2*n] gt 0]

(PARI) isok(n) = fordiv(n, d, if (sigma(d) == 2*n, return(1))); 0; \\ Michel Marcus, May 12 2019

CROSSREFS

Cf. A000203, A000396, A007691, A054030, A323652, A325637.

Sequence in context: A351440 A325637 A336702 * A201186 A060286 A000396

Adjacent sequences: A325651 A325652 A325653 * A325655 A325656 A325657

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, May 12 2019

EXTENSIONS

More terms from Jinyuan Wang, Jun 09 2019

STATUS

proposed