A054985 Composite numbers x such that sigma(x+120) = sigma(x)+120.

182, 203, 287, 350, 407, 558, 611, 731, 779, 803, 963, 1424, 1643, 2627, 2747, 3431, 3806, 4187, 4223, 5063, 6767, 7946, 8927, 9047, 11904, 12707, 12878, 15794, 18923, 20567, 27263, 31175, 32111, 34427, 43139, 43811, 45854, 50165, 52592, 57479

Offset: 1

Author

Labos Elemer, May 29 2000

Keywords

• nonn

Comments

See also A015914, A054799, A033560.

Examples

			a(6)=558, sigma(558)+120=1248+120=1368=sigma(678)=sigma(558+120).
		

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A015914-A015917, A054799.

Programs

Mathematica

Select[Range[60000],CompositeQ[#]&&DivisorSigma[1,#]+120 == DivisorSigma[ 1,#+120]&] (* Harvey P. Dale, Nov 25 2022 *)

PARI

isok(n) = !isprime(n) && (sigma(n+120) == (sigma(n) + 120)); \\ Michel Marcus, Dec 31 2013