A180348 Lexicographically earliest sequence such that a(n) is coprime to the preceding 4 terms and does not occur earlier; a(n) = n for n=1,2,3,4.

1, 2, 3, 4, 5, 7, 11, 9, 8, 13, 17, 19, 15, 14, 23, 29, 31, 25, 6, 37, 41, 43, 35, 12, 47, 53, 59, 49, 10, 27, 61, 67, 71, 16, 21, 55, 73, 79, 26, 51, 77, 83, 89, 20, 39, 97, 101, 103, 22, 45, 91, 107, 109, 32, 33, 65, 113, 119, 38, 69, 121, 125, 127, 28, 57, 131, 85, 137, 44, 63, 139, 95, 149, 34, 81, 143, 115, 133, 58

Offset: 1

Author

M. F. Hasler, Jan 18 2011

Keywords

• nonn

Comments

One possible generalization of A084937 resp. A103683 to N=4, cf. A143345 for a different version.

Programs

PARI

N=99; print1("1, 2, 3"); a=[1, 2, 3, L=4]; unused=[]; v=vector(#a, i, 1); for(n=#a, N, print1(", "a[#a]); for(i=1, #unused, apply(x->gcd(x, unused[i]), a)==v || next; a=concat(vecextract(a, "^1"), unused[i]); unused=vecextract(unused, Str("^", i)); next(2)); L++; while(apply(x->gcd(x, L), a) !=v, unused=concat(unused, L++-1); ); a=concat(vecextract(a, "^1"), L))