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 A340419 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. 5
 397, 157608, 78804, 39402, 19701, 19700, 9850, 4925, 4924, 2462, 1231, 1515360, 757680, 378840, 189420, 94710, 47355, 47354, 23677, 560600328, 280300164, 140150082, 70075041, 70075040, 35037520, 17518760, 8759380, 4379690, 2189845, 2189844, 1094922, 547461 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS It is not known if this sequence reaches the value 1 and stops, or if it enters a cycle or diverges. LINKS Rémy Sigrist, Table of n, a(n) for n = 0..3998 EXAMPLE a(0) = 397 is an odd prime, so a(1) = 397^2 - 1 = 157608. a(1) = 157608 is even, so a(2) = a(1)/2 = 78804. PROG (PARI) v=397; for (n=1, 32, print1 (v", "); v=if (v%2==0, v/2, isprime(v), v^2-1, v-1)) CROSSREFS Cf. A339991, A340008. Sequence in context: A152309 A298124 A327592 * A191942 A158316 A236713 Adjacent sequences:  A340416 A340417 A340418 * A340420 A340421 A340422 KEYWORD nonn,easy,look AUTHOR Rémy Sigrist, Jan 07 2021 STATUS approved

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Last modified May 28 16:37 EDT 2022. Contains 354119 sequences. (Running on oeis4.)