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A136181 Irregular array read by rows: row n contains the LCMs of each pair of consecutive positive divisors of n. 5

%I #23 Mar 13 2018 04:48:45

%S 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,

%T 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,

%U 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

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

%C 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.

%H Diana Mecum, <a href="/A136181/b136181.txt">Table of n, a(n) for n = 2..6070</a>

%e 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).

%e Irregular array begins:

%e 2;

%e 3;

%e 2, 4;

%e 5;

%e 2, 6, 6;

%e 7;

%e 2, 4, 8;

%e 3, 9;

%e 2, 10, 10;

%e 11;

%e 2, 6, 12, 12, 12;

%e ...

%t Flatten[Table[LCM@@@(Partition[Divisors[n],2,1]),{n,2,35}]] (* _Harvey P. Dale_, Apr 22 2011 *)

%o (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

%Y Cf. A027750, A136178, A136182, A136183.

%K nonn,tabf

%O 2,1

%A _Leroy Quet_, Dec 19 2007

%E a(24)-a(85) from _Diana L. Mecum_, Dec 29 2008

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Last modified March 28 17:42 EDT 2024. Contains 371254 sequences. (Running on oeis4.)