A132421 a(n) = LCM of the integers b(k), over all k where 1 <= k <= n, where b(k) = the k-th integer from among those positive integers which are coprime to (n+1-k).

1, 2, 3, 20, 420, 90, 1155, 6552, 990, 340340, 38798760, 406980, 314954640, 30630600, 489304530, 18357939600, 21649708080, 2872543794120, 181957885200, 5555594444400, 237972194460, 32681613985020, 378270916143120, 892567605600, 392636231914726800, 1707200400597892200, 1079806447472472720, 4176841288170450900

Offset

1,2

Comments

a(n) is the LCM of the terms in the n-th antidiagonal of the A126572 array. - Michel Marcus, Mar 14 2018

Links

Table of n, a(n) for n=1..28.

Example

The integers coprime to 4 are 1,3,5,... The first of these is 1. The integers coprime to 3 are 1,2,4,5,... The 2nd of these is 2. The integers coprime to 2 are 1,3,5,7,9,... The 3rd of these is 5. And the integers coprime to 1 are 1,2,3,4,5,... The 4th of these is 4. So a(5) = lcm(1,2,5,4) = 20.

Prog

(PARI) cop(k, j) = {my(nbc = 0, i = 0); while (nbc != j, i++; if (gcd(i, k)==1, nbc++)); i; }
a(n) = lcm(vector(n, k, cop(k, n-k+1))); \\ Michel Marcus, Mar 14 2018

Crossrefs

Cf. A126572, A130767.

Sequence in context: A349600 A110372 A292866 * A132500 A129411 A124447

Adjacent sequences: A132418 A132419 A132420 * A132422 A132423 A132424

Keyword

nonn

Author

Leroy Quet, Aug 20 2007

Extensions

More terms from Sean A. Irvine, Nov 25 2010

Status

approved