OFFSET
0,2
COMMENTS
In other words, a minimal sequence representing a square array (read by antidiagonals) in which every number is coprime to all four closest neighbors. - Ivan Neretin, Jun 05 2015
LINKS
Ivan Neretin, Table of n, a(n) for n = 0..5049
EXAMPLE
T(3,2)=9 is smallest as-yet-unused positive integer coprime to both T(2,1)=7 and T(2,2)=4.
T(4,0)=13 is smallest as-yet-unused positive integer coprime to T(3,0)=6.
Triangle begins:
1
2, 3
5, 7, 4
6, 8, 9, 11
13,17,19,10,12
14,15,16,21,23,25
MATHEMATICA
a[0, 0] = 1; a[m_, n_] := a[m, n] = Block[{k = 2, p = Sort[ Flatten[ Join[ Table[ a[i, j], {i, 0, m - 1}, {j, 0, i}], Table[ a[i, j], {i, m, m}, {j, 0, n - 1}]] ]]}, While[ Position[p, k] != {} || If[n == 0, GCD[k, a[m - 1, 0]] != 1, If[n == m, GCD[k, a[m - 1, m - 1]] != 1, GCD[k, a[m - 1, n]] != 1 || GCD[k, a[m - 1, n - 1]] != 1]], k++ ]; k]; Flatten[ Table[ a[m, n], {m, 0, 10}, {n, 0, m}]] (* Robert G. Wilson v, Sep 04 2004 *)
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Leroy Quet, Sep 02 2004
EXTENSIONS
More terms from Robert G. Wilson v, Sep 04 2004
STATUS
approved