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The October issue of the Notices of the Amer. Math. Soc. has an article about the OEIS.

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A090252 a(n) is the least positive number not already used that is coprime to the previous floor(n/2) terms. 4
1, 2, 3, 5, 4, 7, 9, 11, 13, 17, 8, 19, 23, 25, 21, 29, 31, 37, 41, 43, 47, 53, 16, 59, 61, 67, 71, 73, 55, 79, 27, 49, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 26, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 85, 121, 223, 227, 57, 229 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) is coprime to the next n terms. - David Wasserman, Oct 24 2005

All values up to a(1000000) are either prime powers or semiprimes; this suggests the sequence is unlikely to be a permutation of the integers.

It appears that a(n) is even iff n = 3*2^k-1 for some k. - N. J. A. Sloane, Nov 01 2014

LINKS

Hugo van der Sanden, Table of n, a(n) for n = 1..1001

Hugo van der Sanden, Perl program to calculate this sequence and A249064 (requires Math::Pari)

Hugo van der Sanden, faster Perl program on github.

EXAMPLE

a(1)=1 follows from the definition.

CROSSREFS

Cf. A084937, A249064.

See A247665 for the case when the numbers are required to be at least 2.

Sequence in context: A081994 A249064 A257489 * A140140 A242693 A119474

Adjacent sequences:  A090249 A090250 A090251 * A090253 A090254 A090255

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Nov 27 2003

EXTENSIONS

More terms from David Wasserman, Oct 24 2005

STATUS

approved

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Last modified September 25 01:17 EDT 2018. Contains 315360 sequences. (Running on oeis4.)