A069146 Numbers m such that m = sigma(abs(k)) - 3k, where k = sigma(m) - 3m.

1248, 1596, 28272, 30240, 32760, 463296, 2178540, 12865770, 23569920, 30998250, 45532800, 142990848, 1379454720, 1912369152, 2623977450, 43861478400, 66433720320, 153003540480, 403031236608, 489622536192, 704575228896

Offset

1,1

Comments

1.5*10^12 < a(22) <= 7834005405696. If 2^k-1 > 3 is a prime (A000023), then 2^(k-1)*3*19*(2^k-1) is a term. - Giovanni Resta, Dec 11 2019

Links

Table of n, a(n) for n=1..21.

Example

Let n = 1248. The sum of the divisors of n is 3528, so k = 3528 - 3*1248 = -216. The sum of the divisors of 216 is 600 and 600 - 3*(-216) = 1248, so 1248 is in the sequence.

Mathematica

Select[Range[5*10^5], DivisorSigma[1, Abs[(k = DivisorSigma[1, #] - 3#)]] -3k == # &] (* Amiram Eldar, Dec 11 2019 *)

Crossrefs

Cf. A000203, A069085, A001065.

Sequence in context: A066696 A195006 A114528 * A251648 A235021 A184500

Adjacent sequences: A069143 A069144 A069145 * A069147 A069148 A069149

Keyword

nonn,more

Author

Jason Earls, Apr 08 2002

Extensions

More terms from David Wasserman, Apr 15 2003

a(12)-a(15) from Amiram Eldar, Dec 11 2019

a(16)-a(21) from Giovanni Resta, Dec 11 2019

Status

approved