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 A349277 Triangle T(n,k), n >= 1, 1 <= k <= n, read by rows, where T(n,k) is the number of permutations p of [n] such that Sum_{j=1..n} j/p(j) is an integer and p(n) = k. 2

%I #26 Nov 13 2021 06:00:06

%S 1,0,1,0,0,1,1,0,0,1,0,0,0,0,2,1,1,2,2,0,2,0,0,0,0,0,0,8,4,4,2,2,0,2,

%T 0,8,18,18,14,18,0,14,0,0,22,113,130,102,135,108,122,0,314,0,104,0,0,

%U 0,0,0,0,0,0,0,0,1128,1152,1166,1130,1078,1334,1182,0,1734,3390,1226,0,1128,0,0,0,0,0,0,0,0,0,0,0,0,14520

%N Triangle T(n,k), n >= 1, 1 <= k <= n, read by rows, where T(n,k) is the number of permutations p of [n] such that Sum_{j=1..n} j/p(j) is an integer and p(n) = k.

%F If n is prime, T(n,k) = 0 for 1 <= k <= n-1.

%F T(n,n) = A073090(n-1).

%e Triangle begins:

%e 1;

%e 0, 1;

%e 0, 0, 1;

%e 1, 0, 0, 1;

%e 0, 0, 0, 0, 2;

%e 1, 1, 2, 2, 0, 2;

%e 0, 0, 0, 0, 0, 0, 8;

%e 4, 4, 2, 2, 0, 2, 0, 8;

%e 18, 18, 14, 18, 0, 14, 0, 0, 22;

%e 113, 130, 102, 135, 108, 122, 0, 314, 0, 104;

%e 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1128;

%o (Ruby)

%o def A(n)

%o ary = Array.new(n, 0)

%o (1..n).to_a.permutation{|i|

%o ary[i[-1] - 1] += 1 if (1..n).inject(0){|s, j| s + j / i[j - 1].to_r}.denominator == 1

%o }

%o ary

%o end

%o def A349277(n)

%o (1..n).map{|i| A(i)}.flatten

%o end

%o p A349277(8)

%Y Row sum gives A073090.

%K nonn,tabl

%O 1,15

%A _Seiichi Manyama_, Nov 12 2021

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Last modified September 8 15:58 EDT 2024. Contains 375753 sequences. (Running on oeis4.)