A340419 - OEIS

%I #16 Jan 07 2021 16:44:00

%S 397,157608,78804,39402,19701,19700,9850,4925,4924,2462,1231,1515360,

%T 757680,378840,189420,94710,47355,47354,23677,560600328,280300164,

%U 140150082,70075041,70075040,35037520,17518760,8759380,4379690,2189845,2189844,1094922,547461

%N Trajectory of 397 under the map A340008: n -> n/2 if n is even, n-> n^2 - 1 if n is an odd prime, otherwise n -> n - 1.

%C It is not known if this sequence reaches the value 1 and stops, or if it enters a cycle or diverges.

%H Rémy Sigrist, <a href="/A340419/b340419.txt">Table of n, a(n) for n = 0..3998</a>

%e a(0) = 397 is an odd prime, so a(1) = 397^2 - 1 = 157608.

%e a(1) = 157608 is even, so a(2) = a(1)/2 = 78804.

%o (PARI) v=397; for (n=1, 32, print1 (v", "); v=if (v%2==0, v/2, isprime(v), v^2-1, v-1))

%Y Cf. A339991, A340008.

%K nonn,easy,look

%O 0,1

%A _Rémy Sigrist_, Jan 07 2021