A249064 - OEIS

%I #19 Nov 01 2014 17:47:50

%S 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,

%T 67,71,73,79,83,89,97,101,103,107,22,109,113,27,35,127,131,137,139,

%U 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

%N Lexically first sequence of distinct positive integers such that a(n) is coprime to the next a(n) elements.

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

%C (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)

%C 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.

%C 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

%H Hugo van der Sanden, <a href="/A249064/b249064.txt">Table of n, a(n) for n = 1..1001</a>

%H Hugo van der Sanden, <a href="/A249064/a249064.txt">Perl program</a> to calculate this sequence and A090252 (requires Math::Pari)

%H Hugo van der Sanden, <a href="https://github.com/hvds/seq/blob/master/A249064/A249064">Faster Perl program</a> on github.

%Y Cf. A090252, A247665, A249557.

%K nonn

%O 1,2

%A _Hugo van der Sanden_, Oct 20 2014

%E Added "distinct" to the definition. - _Hugo van der Sanden_, Oct 28 2014