A048133 Least number which becomes prime or 4 after exactly n iterations of f(x) = sum of prime factors of x.

2, 6, 8, 14, 26, 62, 134, 393, 1257, 4659, 9314, 27933, 167073, 334142, 4677862, 14033577, 56134292, 2133102298, 11788191218, 52541651594, 536226160966, 2681130804805, 8512643845707, 129535245187539

Offset: 0

Author

David W. Wilson

Keywords

• nonn
• more

Comments

f(x) = sum of prime factors with multiplicity, so that f(1500) = 2+2+3+5+5+5 = 22.

Identical to the different-offset A121360 except for the second term. - Hans Havermann, Oct 05 2010

a(20) <= 536226160966. a(21) <= 2681130804805. a(22) <= 8512643845707. - Donovan Johnson, Oct 16 2010

a(24) <= 1679460336114602. - Danila Potapov, Dec 01 2024

Crossrefs

Cf. A121360 .

Extensions

a(17) from Donovan Johnson, Apr 25 2010

a(18)-a(19) from Donovan Johnson, Oct 16 2010

a(20)-a(23) from Danila Potapov, Dec 01 2024