OFFSET
1,1
COMMENTS
Values are tested for natural numbers up to 1000000.
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, E16.
LINKS
T. D. Noe, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1) = 42 = total number of k such that k-1 appears in the Collatz sequence of k, that is, the number of terms in A070991.
MATHEMATICA
Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; nn = 75; t = Table[0, {nn}]; lastChange = 10; k = 0; While[k < 2*lastChange, k++; c = Collatz[k]; d = Intersection[Range[nn], k - c]; If[Length[d] > 0, lastChange = k; t[[d]]++]]; t (* T. D. Noe, Feb 21 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jayanta Basu, Feb 21 2013
STATUS
approved