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A070994
Numbers k such that the trajectory of k under the 3x+1 map reaches phi(k).
1
2, 3, 4, 5, 6, 8, 10, 11, 12, 15, 16, 17, 20, 22, 24, 25, 30, 32, 33, 34, 40, 41, 44, 47, 48, 50, 55, 59, 60, 64, 66, 71, 82, 85, 87, 88, 89, 94, 100, 107, 110, 118, 128, 132, 142, 164, 165, 170, 174, 178, 188, 214, 220, 235, 256, 328, 330, 340, 348, 376, 440, 470
OFFSET
1,1
COMMENTS
If k is a power of 2, then k is in the sequence.
LINKS
EXAMPLE
The trajectory of 10 is: (10,5,16,8,4,2,1) and phi(10) = 4 is reached, hence 10 is in the sequence.
MATHEMATICA
c[n_] := If[OddQ[n], 3*n + 1, n/2]; q[2] = True; q[n_] := NestWhile[c, n, # != EulerPhi[n] && # > 1 &] > 1; Select[Range[500], q] (* Amiram Eldar, Apr 29 2022 *)
PROG
(PARI) for(n=1, 10000, s=n; t=0; while(s!=1, t++; if(s%2==0, s=s/2, s=3*s+1); if(s==eulerphi(n), print1(n, ", "); ); ))
CROSSREFS
Sequence in context: A182625 A333909 A088232 * A291686 A057197 A067936
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, May 18 2002
STATUS
approved