OFFSET
3,1
LINKS
Eric W. Weisstein, Table of n, a(n) for n = 3..90
Eric Weisstein's World of Mathematics, Erdős Graph.
Eric W. Weisstein, Illustration
EXAMPLE
C_4 has Erdős sequence (10,14,15,21) since the pairs sharing factors are 10~14 (sharing 2), 14~21 (sharing 7), 21~15 (sharing 3), 15~10 (sharing 5), which correspond to the edges of the 4-cycle graph, 21 is the smallest possible maximum value for such a sequence, and (10,14,15,21) is the lexicographically first such sequence.
Triangle begins:
2, 4, 6;
10, 14, 15, 21;
10, 21, 22, 33, 35;
14, 26, 33, 35, 39, 55;
14, 34, 39, 51, 55, 65, 77;
22, 38, 51, 57, 65, 77, 85, 91;
22, 34, 39, 69, 95, 115, 119, 133, 143;
PROG
(PARI) row(n)=if(n<4, if(n==3, [2, 4, 6]), my(v=[oo]); forperm(primes(n), p, my(t=vecsort(vector(#p, k, p[k]*if(k==1, p[#p], p[k-1])))); if(t[#t] < v[#v] || (t[#t] == v[#v] && lex(t, v)<0), v=t)); v) \\ Andrew Howroyd, Feb 25 2024
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
Eric W. Weisstein, Feb 24 2024
EXTENSIONS
a(45)-a(65) from Andrew Howroyd, Feb 25 2024
STATUS
approved