

A263411


"Shuffled bisection" of positive even and odd numbers, type 1 (see "Comments" for rules generating the sequence).


1



1, 3, 5, 7, 2, 9, 11, 13, 4, 15, 17, 19, 6, 8, 21, 23, 10, 12, 25, 14, 27, 29, 31, 16, 33, 35, 37, 18, 20, 39, 41, 43, 22, 45, 47, 24, 49, 26, 51, 53, 28, 55, 57, 59, 61, 30, 32, 63, 34, 65, 67, 36, 38, 69, 71, 73, 40, 42, 44, 75, 46, 77, 79, 48, 50
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OFFSET

1,2


COMMENTS

All terms are positive, with even and odd terms appearing in due course in order. One might think of the sequence as the result of two poorlyshuffled decks of cards with numbers in increasing order  one deck with all the positive even numbers and one with all the positive odd numbers, following this set of rules:
Start with a(1)=1; take next odd number until preceding an odd composite; then take next even number if coprime to last term, otherwise take next odd. If even term is selected, take next odd unless coprime to last term, otherwise take next even. Repeat indefinitely.
Odd terms precede primes (by definition); primes are followed by even terms unless smallest twin prime.
Is there a limit to the maximum length of odd or even strings?
Same as A263792(n), n <= 25.
If seeds are a(1)=1 and a(2)=2, the sequences converge after a(17).


LINKS

Table of n, a(n) for n=1..65.


EXAMPLE

a(7)=11; since next odd is prime, take a(8)=13. Since next odd is composite and next even (4) is coprime to 13, take a(9)=4.
a(24)=16; since next odd (33) is coprime to 16, take a(25)=33. Since next odd is composite we consider next even (18) as next term; but since 18 is not coprime to 33, instead we take a(26)=35.


CROSSREFS

Cf. A005408, A005843, A263792.
Sequence in context: A104260 A334355 A263792 * A121573 A196407 A156030
Adjacent sequences: A263408 A263409 A263410 * A263412 A263413 A263414


KEYWORD

nonn


AUTHOR

Bob Selcoe, Oct 26 2015


STATUS

approved



