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a(n) = (1/n)*(product of the terms of the n-th row of A177028).
3

%I #12 Mar 24 2021 06:04:49

%S 1,1,1,3,1,1,4,3,1,5,1,1,18,4,1,7,1,1,24,5,1,9,4,1,10,18,1,11,1,1,12,

%T 7,5,156,1,1,14,8,1,15,1,1,288,9,1,17,4,1,90,10,1,19,21,1,20,11,1,21,

%U 1,1,22,48,8,414,1,1,24,65,1,25,1,1,234,14,1,81,1,1,784,15

%N a(n) = (1/n)*(product of the terms of the n-th row of A177028).

%H Michel Marcus, <a href="/A342805/b342805.txt">Table of n, a(n) for n = 3..10000</a>

%F For m in A090466, a(m) > 1.

%F For m in A090467, a(m) = 1.

%e For n=3, A177028 row is (3), so a(3) = 3/3 = 1.

%e For n=6, A177028 row is (6, 3), so a(6) = 6*3/6 = 3.

%e For n=15, A177028 row is (15, 6, 3), so a(15) = 15*6*3/15 = 18.

%o (PARI) row(n)=my(v=List()); fordiv(2*n, k, if(k<2, next); if(k==n, break); my(s=(2*n/k-4+2*k)/(k-1)); if(denominator(s)==1, listput(v, s))); Vec(v); \\ A177028

%o a(n) = vecprod(row(n))/n;

%Y Cf. A090466, A090467, A177028, A342772.

%K nonn

%O 3,4

%A _Michel Marcus_, Mar 22 2021