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

2,1

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.

Links

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

Example

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;
...

Mathematica

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

Prog

(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

Crossrefs

Cf. A027750, A136178, A136182, A136183.

Sequence in context: A214540 A214595 A357255 * A265110 A304742 A003976

Adjacent sequences: A136178 A136179 A136180 * A136182 A136183 A136184

Keyword

nonn,tabf

Author

Leroy Quet, Dec 19 2007

Extensions

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

Status

approved