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A141327 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). 7
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, 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, 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 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

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

LINKS

Diana Mecum, Table of n, a(n) for n=2..1276

FORMULA

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) }.

EXAMPLE

Array begins:

2 6 2 10 2 14 2 18 ...

6 3 6 15 6 ...

2 6 2 10 ...

10 15 ...

2 ...

MATHEMATICA

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 *)

CROSSREFS

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

Sequence in context: A175994 A340212 A283613 * A248011 A282729 A011386

Adjacent sequences:  A141324 A141325 A141326 * A141328 A141329 A141330

KEYWORD

nonn,tabl

AUTHOR

Leroy Quet, Jun 25 2008

EXTENSIONS

Edited by N. J. A. Sloane, Dec 28 2008

Extended by Ray Chandler, Jun 24 2009

STATUS

approved

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Last modified October 21 11:51 EDT 2021. Contains 348150 sequences. (Running on oeis4.)