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A249064 Lexically first sequence of distinct positive integers such that a(n) is coprime to the next a(n) elements. 4
1, 2, 3, 5, 4, 7, 9, 11, 13, 8, 17, 19, 23, 25, 29, 31, 21, 37, 16, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 22, 109, 113, 27, 35, 127, 131, 137, 139, 149, 151, 157, 163, 167, 169, 173, 179, 181, 191, 193, 197, 199, 211, 32, 121, 223, 227, 229, 233, 239, 241, 51, 251, 257, 263, 269, 271, 277, 281, 283, 49, 95 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Described in this form, A090252 would be "lexically first sequence of positive integers such that a(n) is coprime to the next n elements".

(And A247665 would be "lexically first sequence of integers >= 2 such that a(n) is coprime to the next n elements". - N. J. A. Sloane, Nov 01 2014)

All values up to a(1000000) are either prime powers or semiprimes, except when n is in (868, 947, 993, 1069, 1205, 1431, 854300) with values respectively (172, 45, 75, 135, 225, 375, 9475). This suggests the sequence is unlikely to be a permutation of the integers.

If, mimicking A247665, one starts with a(1)=2 and uses the same rule (always using distinct numbers >= 2) one obtains A249064 again, without the leading 1. - 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 A090252 (requires Math::Pari)

Hugo van der Sanden, Faster Perl program on github.

CROSSREFS

Cf. A090252, A247665, A249557.

Sequence in context: A084937 A269367 A081994 * A257489 A090252 A140140

Adjacent sequences:  A249061 A249062 A249063 * A249065 A249066 A249067

KEYWORD

nonn

AUTHOR

Hugo van der Sanden, Oct 20 2014

EXTENSIONS

Added "distinct" to the definition. - Hugo van der Sanden, Oct 28 2014

STATUS

approved

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Last modified November 14 09:49 EST 2018. Contains 317182 sequences. (Running on oeis4.)