A136181 Irregular array read by rows: row n contains the LCMs of each pair of consecutive positive divisors of n.

2, 3, 2, 4, 5, 2, 6, 6, 7, 2, 4, 8, 3, 9, 2, 10, 10, 11, 2, 6, 12, 12, 12, 13, 2, 14, 14, 3, 15, 15, 2, 4, 8, 16, 17, 2, 6, 6, 18, 18, 19, 2, 4, 20, 10, 20, 3, 21, 21, 2, 22, 22, 23, 2, 6, 12, 12, 24, 24, 24, 5, 25, 2, 26, 26, 3, 9, 27, 2, 4, 28, 14, 28, 29, 2, 6, 15, 30, 30, 30, 30, 31, 2, 4

Offset: 2

Author

Leroy Quet, Dec 19 2007

Keywords

• nonn
• tabf

Comments

Each row has d(n)-1 terms, where d(n) is the number of positive divisors of n. The first row listed is row 2.

Examples

			The positive divisors of 20 are 1,2,4,5,10,20; lcm(1,2)=2, lcm(2,4)=4, lcm(4,5)=20, lcm(5,10)=10, and lcm(10,20)=20, so row 20 is (2,4,20,10,20).
Irregular array begins:
  2;
  3;
  2, 4;
  5;
  2, 6, 6;
  7;
  2, 4, 8;
  3, 9;
  2, 10, 10;
 11;
  2, 6, 12, 12, 12;
...
		

Links

• Diana Mecum, Table of n, a(n) for n = 2..6070

Crossrefs

Cf. A027750, A136178, A136182, A136183.

Programs

Mathematica

Flatten[Table[LCM@@@(Partition[Divisors[n],2,1]),{n,2,35}]]  (* Harvey P. Dale, Apr 22 2011 *)

PARI

tabf(nn) = {for (n=2, nn, d = divisors(n); for (k=2, #d, print1(lcm(d[k-1], d[k]), ", ");); print;);} \\ Michel Marcus, Mar 13 2018

Extensions

a(24)-a(85) from Diana L. Mecum, Dec 29 2008