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Least number which becomes prime or 4 after exactly n iterations of f(x) = sum of prime factors of x.
5

%I #13 Dec 02 2024 18:13:33

%S 2,6,8,14,26,62,134,393,1257,4659,9314,27933,167073,334142,4677862,

%T 14033577,56134292,2133102298,11788191218,52541651594,536226160966,

%U 2681130804805,8512643845707,129535245187539

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

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

%C Identical to the different-offset A121360 except for the second term. - _Hans Havermann_, Oct 05 2010

%C a(20) <= 536226160966. a(21) <= 2681130804805. a(22) <= 8512643845707. - _Donovan Johnson_, Oct 16 2010

%C a(24) <= 1679460336114602. - _Danila Potapov_, Dec 01 2024

%Y Cf. A121360 .

%K nonn,more

%O 0,1

%A _David W. Wilson_

%E a(17) from _Donovan Johnson_, Apr 25 2010

%E a(18)-a(19) from _Donovan Johnson_, Oct 16 2010

%E a(20)-a(23) from _Danila Potapov_, Dec 01 2024