cp's OEIS Frontend

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).

%I A132421 #19 Mar 14 2018 04:26:18
%S A132421 1,2,3,20,420,90,1155,6552,990,340340,38798760,406980,314954640,
%T A132421 30630600,489304530,18357939600,21649708080,2872543794120,
%U A132421 181957885200,5555594444400,237972194460,32681613985020,378270916143120,892567605600,392636231914726800,1707200400597892200,1079806447472472720,4176841288170450900
%N 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).
%C A132421 a(n) is the LCM of the terms in the n-th antidiagonal of the A126572 array. - _Michel Marcus_, Mar 14 2018
%e A132421 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.
%o A132421 (PARI) cop(k, j) = {my(nbc = 0, i = 0); while (nbc != j, i++; if (gcd(i,k)==1, nbc++)); i;}
%o A132421 a(n) = lcm(vector(n, k, cop(k, n-k+1))); \\ _Michel Marcus_, Mar 14 2018
%Y A132421 Cf. A126572, A130767.
%K A132421 nonn
%O A132421 1,2
%A A132421 _Leroy Quet_, Aug 20 2007
%E A132421 More terms from _Sean A. Irvine_, Nov 25 2010