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A216625
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Triangle read by rows, n >= 1, 1 <= k <= n, T(n,k) = Sum_{c|n,d|k} gcd(c,d).
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8
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1, 2, 5, 2, 4, 6, 3, 8, 6, 15, 2, 4, 4, 6, 8, 4, 10, 12, 16, 8, 30, 2, 4, 4, 6, 4, 8, 10, 4, 11, 8, 22, 8, 22, 8, 37, 3, 6, 10, 9, 6, 20, 6, 12, 23, 4, 10, 8, 16, 16, 20, 8, 22, 12, 40, 2, 4, 4, 6, 4, 8, 4, 8, 6, 8, 14, 6, 16, 18, 30, 12, 48, 12, 44, 30, 32
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OFFSET
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1,2
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COMMENTS
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This is the lower triangular array of A216624, which is the main entry for this sequence.
T(n,n) = A060724(n) = Sum_{d|n} d*tau((n/d)^2).
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LINKS
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EXAMPLE
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The first rows of the triangle are:
1;
2, 5;
2, 4, 6;
3, 8, 6, 15;
2, 4, 4, 6, 8;
4, 10, 12, 16, 8, 30;
2, 4, 4, 6, 4, 8, 10;
4, 11, 8, 22, 8, 22, 8, 37;
3, 6, 10, 9, 6, 20, 6, 12, 23;
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MAPLE
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with(numtheory):
T:= (n, k)-> add(add(igcd(c, d), c=divisors(n)), d=divisors(k)):
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MATHEMATICA
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T[n_, k_] := Sum[GCD[c, d], {c, Divisors[n]}, {d, Divisors[k]}]; Table[T[n, k], {n, 1, 14}, {k, 1, n}] // Flatten (* Jean-François Alcover, Mar 25 2014 *)
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PROG
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(Sage)
for n in (1..9): [A216624(n, k) for k in (1..n)]
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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