A078543 Balanced refactorable numbers.

1, 2, 12, 56, 248, 12192, 28896, 60960, 61344, 66528, 86304, 94944, 129504, 133920, 140448, 182880, 201924, 207264, 242316, 282720, 408672, 416640, 426720, 429408, 604128, 664608, 671760, 776736, 792480, 854496, 862752, 906528

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000 (calculated using data from Jud McCranie, terms 1..500 from Donovan Johnson)

Example

n=56: tau(56)=8, sigma(56)=120, phi(56)=24, q1=120/24=5 for balancedness, q2=56/8=7 for refactorability.

Mathematica

Do[s=DivisorSigma[1, n]/EulerPhi[n]; If[ !IntegerQ[s]&&!PrimeQ[n], Print[n]], {n, 1, 256}]

Crossrefs

Intersection of A033950 and A020492.

Cf. A078538, A078539, A078540.

Sequence in context: A037130 A181298 A247121 * A084128 A044047 A296944

Adjacent sequences: A078540 A078541 A078542 * A078544 A078545 A078546

Keyword

nonn

Author

Labos Elemer, Dec 04 2002

Status

approved