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 A067579 Conjectured values of a(n) defined by: a(n) = first prime appearing in the orbit n, f(n), f(f(n)),...., if it exists; = 0 otherwise, where f(n) = n + sigma(n). 0

%I #3 Feb 11 2014 19:05:26

%S 2,2,3,11,5,137,7,23,0,0,11,0,13,269,479,47,17,137,19,61223,53,0,23,0,

%T 0,0,67,0,29,0,31,479,0,0,83,127,37,269,479,0

%N Conjectured values of a(n) defined by: a(n) = first prime appearing in the orbit n, f(n), f(f(n)),...., if it exists; = 0 otherwise, where f(n) = n + sigma(n).

%C The values n with a(n) = 0 listed here are conjectural. There is no prime < 10^30 appearing in the orbits of these values.

%e The orbit of 4 is 4, 11, 23,.... and the first prime in the orbit is 11. So a(4) = 11.

%t f[ n_ ] := n + DivisorSigma[ 1, n ]; h[ n_ ] := Module[ { a = n}, While[ ! PrimeQ[ a ] && a < 10^30, a = f[ a ] ]; If [ ! PrimeQ[ a ], a = 0 ]; a ]; Table[ h[ i ], {i, 1, 40} ]

%K nonn

%O 1,1

%A _Joseph L. Pe_, Jan 30 2002

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Last modified September 29 13:10 EDT 2023. Contains 365771 sequences. (Running on oeis4.)