OFFSET
0,1
COMMENTS
27=A060412(4); a(A006577(27))=a(111)=1; a(n)=A161021(n+59) for n with 103<=n<=111. - Reinhard Zumkeller, Jun 03 2009
At step 109 enters the loop 4 2 1 4 2 1 4 2 1 ... - N. J. A. Sloane, Jul 27 2019
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, E16.
H.-O. Peitgen et al., Chaos and Fractals, Springer, p. 33.
LINKS
T. D. Noe, Table of n, a(n) for n = 0..111
F. Oort, Prime numbers, 2013, ICCM Notices, Talk at Academia Sinica and National Taiwan University, 17-XII-2012.
Index entries for linear recurrences with constant coefficients, signature (0,0,1).
FORMULA
a(0) = 27, a(n) = 3*a(n-1)+1 if a(n-1) is odd, a(n) = a(n-1)/2 if a(n-1) is even. - Vincenzo Librandi, Dec 24 2010; corrected by Klaus Brockhaus, Dec 25 2010
MAPLE
f := proc(n) option remember; if n = 0 then 27; elif f(n-1) mod 2 = 0 then f(n-1)/2 else 3*f(n-1)+1; fi; end;
MATHEMATICA
NestList[If[EvenQ[#], #/2, 3#+1]&, 27, 70] (* Harvey P. Dale, Jun 30 2011 *)
PROG
(Magma) [ n eq 1 select 27 else IsOdd(Self(n-1)) select 3*Self(n-1)+1 else Self(n-1) div 2: n in [1..70] ]; // Klaus Brockhaus, Dec 25 2010
(PARI) Collatz(n, lim=0)={
my(c=n, e=0, L=List(n)); if(lim==0, e=1; lim=n*10^6);
for(i=1, lim, if(c%2==0, c=c/2, c=3*c+1); listput(L, c); if(e&&c==1, break));
return(Vec(L)); }
print(Collatz(27)) \\ A008884 (from 27 to the first 1)
\\ Anatoly E. Voevudko, Mar 26 2016
CROSSREFS
KEYWORD
nonn,nice,easy
AUTHOR
EXTENSIONS
More terms from Larry Reeves (larryr(AT)acm.org), Apr 27 2001
STATUS
approved