login
A136181
Irregular array read by rows: row n contains the LCMs of each pair of consecutive positive divisors of n.
5
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.
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
KEYWORD
nonn,tabf
AUTHOR
Leroy Quet, Dec 19 2007
EXTENSIONS
a(24)-a(85) from Diana L. Mecum, Dec 29 2008
STATUS
approved