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 A261814 a(n) = smallest initial value s such that n is in the Collatz trajectory of s (s is not regarded as part of its trajectory). 1
 2, 3, 6, 3, 3, 12, 9, 3, 18, 3, 7, 24, 7, 9, 30, 3, 7, 36, 25, 7, 42, 7, 15, 48, 33, 7, 54, 9, 19, 60, 27, 21, 66, 7, 15, 72, 43, 25, 78, 7, 27, 84, 57, 19, 90, 15, 27, 96, 43, 33, 102, 7, 15, 108, 73, 37, 114, 19, 39, 120, 27, 27, 126, 21, 43, 132, 39, 45 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The initial term is not counted as an element of the trajectory. For even n obviously a(n) <= 2n, because the halving step would reach n. - R. J. Mathar, Nov 27 2015 LINKS Michel Lagneau, Table of n, a(n) for n = 1..5000 EXAMPLE a(1)=2 because the number 1 is in the trajectory 2 -> 1; a(2)=3 because the number 2 is in the trajectory 3 -> 10 -> 5 -> ... -> 2 -> 1; a(3)=6 because the number 3 is in the trajectory 6 -> 3 -> 10 -> ... -> 1; a(4)=3 because the number 4 is in the trajectory 3 -> 10 -> 5 -> ... -> 4 -> 2 -> 1. MAPLE Collatz := proc(n)     if type(n, 'even') then         n/2;     else         3*n+1 ;     end if; end proc: CollatzTrj := proc(x, membSrch)     local t;     t := x ;     while t <> 1 do         t := Collatz(t) ;         if t = membSrch then             return true ;         end if;     end do:     return false; end proc: A261814 := proc(n)     for x from 2 do         if CollatzTrj(x, n) then             return x;         end if;     end do; end proc: # R. J. Mathar, Nov 27 2015 CROSSREFS Cf. A006577, A260303, A260389. Sequence in context: A245886 A224504 A216059 * A240965 A084228 A328571 Adjacent sequences:  A261811 A261812 A261813 * A261815 A261816 A261817 KEYWORD nonn AUTHOR Michel Lagneau, Nov 22 2015 STATUS approved

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Last modified April 6 22:23 EDT 2020. Contains 333291 sequences. (Running on oeis4.)