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 A291939 First number on layer n of hailstone chain. 1
 1, 12, 19, 27, 37, 43, 51, 55, 75, 79, 93, 102, 109, 115, 120, 127, 133, 141, 147, 151, 156, 163, 177, 181, 186, 199, 217, 223, 235, 241, 249, 255, 259, 264, 271, 277, 282, 294, 307, 312, 315, 324, 331, 343, 345, 349, 354, 357, 363, 367 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If hailstone chains are strictly drawn in numerical order at right angles with consistent direction, overlaps occur. The first set of numbers that do not overlap could be considered the 'first layer'. Once an overlap is needed, all numbers farther up the chain (inclusive) are on a higher layer. This is the sequence of the first numbers to appear on layer n. From Georg Fischer, Mar 25 2018: (Start) The detailed procedure is as follows: Take the "3x+1" or Collatz sequences (CSs) from A070165, and build a 3-dimensional structure representing all CSs up to some starting number (10000). In that 3D structure, the y direction is downwards, x is to the right, and the "layer" z is outside. Process all CSs with increasing starting number coln = 1, 2, 3, ..., 10000. Begin at the end of any individual CS (4, 2, 1), and proceed backwards up to the starting number. Name the elements e[1] = 1, e[2] = 2, e[3] = 4, etc. Position the element e[1] = 1 at coordinates (x,y,z) = (0,0,0). Investigate all e[i] (i > 1): for even e[i] "go right" = store e[i] at (e[i-1].x+1, e[i-1].y, e[i-1].z), for odd e[i] "go down" = store e[i] at (e[i-1].x, e[i-1].y+1, e[i-1].z), whenever that position is not occupied by a different number, otherwise "go out", i.e., increase the layer z by one for this element and all new elements to be stored from now on. The present sequence A291939 = a(n) consists of the starting values of the CSs which reach a z coordinate of n for the first time. (End) LINKS Georg Fischer, Table of n, a(n) for n = 1..1769 Georg Fischer, Description, generating Perl program and 3D visualization EXAMPLE n=1: the first number is trivially 1; n=2: in the CS for 12, the 12 overlaps with 13, thus 12 is on layer 2; n=3: in the CS for 19, the 44 overlaps with 46, thus 19 is on layer 3. CROSSREFS Cf. A006370, A070165. Sequence in context: A003335 A030609 A053752 * A043102 A039279 A045067 Adjacent sequences:  A291936 A291937 A291938 * A291940 A291941 A291942 KEYWORD nonn,easy AUTHOR Jonathan Llewellyn, Sep 06 2017 EXTENSIONS More terms from Georg Fischer, Mar 25 2018 STATUS approved

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Last modified May 26 02:56 EDT 2020. Contains 334613 sequences. (Running on oeis4.)