A048133 - OEIS

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

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OFFSET

0,1

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

LINKS

CROSSREFS

KEYWORD

nonn

AUTHOR

EXTENSIONS

a(17) from Donovan Johnson, Apr 25 2010

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

STATUS

approved