A244638 - OEIS

A244638

In the '3x+1' problem, primes which as starting values set new records for number of steps to reach 1, where a step means either 'divide by two' or 'triple plus one and then divide by two'.

2, 3, 7, 19, 31, 41, 73, 97, 193, 257, 313, 487, 859, 937, 1249, 2539, 3331, 3947, 5351, 5839, 7963, 9257, 12343, 21943, 31687, 45127, 60169, 78791, 115547, 180463, 213881, 234239, 270271, 376603, 875681, 1023871, 1252663, 1564063, 2585279, 4063723, 5649499, 9973919, 11200681, 39824647, 41464303, 73583071, 95592191, 226588897, 1359533387, 2263333321, 3349304527

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..51.

Wikipedia, Collatz Conjecture

Index entries for sequences related to 3x+1 (or Collatz) problem

MATHEMATICA

f[n_] := Length@ NestWhileList[ If[ OddQ@ #, (3 # + 1)/2, #/2] &, n, # > 1 &] mx = 0; p = 2; lst = {}; While[p < 10^10/2, a = f@ p; If[a > mx, mx = a; Print[{PrimePi@p, p, a - 1}]; AppendTo[ lst, p]]; p = NextPrime@ p]; lst

CROSSREFS

Cf. A006877, A006577, A006884.

Sequence in context: A174568 A005382 A195354 * A113165 A128025 A092064

Adjacent sequences: A244635 A244636 A244637 * A244639 A244640 A244641

KEYWORD

nonn

AUTHOR

Zak Seidov and Robert G. Wilson v, Jul 03 2014

STATUS

approved