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A261702 a(1) = 1; for n>1, a(n) is the smallest positive integer not already present which is entailed by the rules (i) k present => 2k present; (ii) 3k+1 present and k odd => k present. 2
1, 2, 4, 8, 16, 5, 10, 3, 6, 12, 20, 24, 32, 40, 13, 26, 48, 52, 17, 34, 11, 22, 7, 14, 28, 9, 18, 36, 44, 56, 64, 21, 42, 68, 72, 80, 84, 88, 29, 58, 19, 38, 76, 25, 50, 96, 100, 33, 66, 104, 112, 37, 74, 116, 128, 132, 136, 45, 90, 144, 148, 49, 98, 152 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
If the Collatz 3n+1 conjecture is true, then this is a permutation of all positive integers. See A261715 for putative inverse.
LINKS
MAPLE
a:= proc() local a, b, s; b, s:= proc() true end,
heap[new]((x, y)-> is(x>y), 1); a:=
proc(n) option remember; local k, t;
if n>1 then a(n-1) fi;
t:= heap[extract](s); b(t):= false;
k:= 2*t; if b(k) then heap[insert](k, s) fi;
if irem(t-1, 3, 'k')=0 and (k::odd) and
b(k) then heap[insert](k, s) fi; t
end
end():
seq(a(n), n=1..80); # Alois P. Heinz, Aug 29 2015
PROG
(Perl) See Links section.
(C++) See Links section.
CROSSREFS
Cf. A088975, A033491, A109732, A261690, A261715 (putative inverse).
Sequence in context: A110001 A302030 A167426 * A033491 A050076 A276070
KEYWORD
nonn,look
AUTHOR
Paul Tek, Aug 28 2015
STATUS
approved

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Last modified March 1 20:05 EST 2024. Contains 370443 sequences. (Running on oeis4.)