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A229487 Conjectured greatest number that converges to prime(n) under the iteration x -> phi(x) + 1, where phi is Euler's totient function. 2
2, 6, 12, 30, 22, 138, 60, 54, 46, 58, 62, 174, 498, 510, 94, 106, 118, 4314, 134, 142, 1038, 158, 166, 276, 420, 250, 206, 214, 750, 1758, 254, 262, 274, 278, 298, 302, 1182, 486, 334, 346, 358, 6360, 382, 1614, 394, 398, 422, 446, 454, 458, 5898, 478, 54582 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Many terms are just twice a prime: 6, 22, 46, 58, 62, 94,....

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..1000

EXAMPLE

The number 138 has trajectory {138, 45, 25, 21, 13}, which is conjecturally the last number that terminates with 13 = prime(6). Hence a(6) = 138.

MATHEMATICA

t = Table[NestWhileList[EulerPhi[#] + 1 &, n, UnsameQ, All][[-1]], {n, 100000}]; Table[Position[t, p][[-1]], {p, Prime[Range[53]]}]

CROSSREFS

Cf. A039650, A039651, A039652.

Sequence in context: A057582 A094779 A093387 * A195166 A225646 A225627

Adjacent sequences:  A229484 A229485 A229486 * A229488 A229489 A229490

KEYWORD

nonn

AUTHOR

T. D. Noe, Oct 16 2013

STATUS

approved

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Last modified November 17 00:02 EST 2018. Contains 317275 sequences. (Running on oeis4.)