A141327 - OEIS

%I #15 Aug 02 2017 10:41:53

%S 2,6,6,2,3,2,10,6,6,10,2,15,2,15,2,14,3,10,10,3,14,2,21,2,5,2,21,2,6,

%T 6,14,10,10,14,6,6,2,3,2,35,2,35,2,3,2,22,6,6,10,14,14,10,6,6,22,2,33,

%U 2,15,2,7,2,15,2,33,2,26,3,22,5,3,14,14,3,5,22,3,26,2,39,2,55,2,21,2,21,2

%N Infinite array read by antidiagonals: a(m,n) = the smallest positive integer that has a factor in common with both m and n (m >= 2, n >= 2).

%C The first row of this array is row 2. The first column of this array is column 2.

%H Diana Mecum, <a href="/A141327/b141327.txt">Table of n, a(n) for n=2..1276</a>

%F If gcd(m,n) = 1 then a(m,n) = smallest prime factor of m times smallest prime factor of n, if gcd(m,n) > 1 then a(m,n) = min { smallest prime factor of m times smallest prime factor of n, smallest prime factor of gcd(m,n) }.

%e Array begins:

%e 2 6 2 10 2 14 2 18 ...

%e 6 3 6 15 6 ...

%e 2 6 2 10 ...

%e 10 15 ...

%e 2 ...

%t Table[k = 2; While[Or[CoprimeQ[#, k], CoprimeQ[n, k]] &[m - n + 2], k++]; k, {m, 2, 14}, {n, 2, m}] // Flatten (* _Michael De Vlieger_, Aug 01 2017 *)

%Y Cf. A141328, A141329. For a triangular version see A144531.

%K nonn,tabl

%O 2,1

%A _Leroy Quet_, Jun 25 2008

%E Edited by _N. J. A. Sloane_, Dec 28 2008

%E Extended by _Ray Chandler_, Jun 24 2009