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A119948 Triangle of denominators in the square of the matrix with A[i,j] = 1/i for j <= i, 0 otherwise. 4
1, 4, 4, 18, 18, 9, 48, 48, 48, 16, 300, 300, 300, 100, 25, 120, 120, 120, 360, 180, 36, 980, 980, 980, 2940, 1470, 294, 49, 2240, 2240, 2240, 6720, 6720, 1344, 448, 64, 22680, 22680, 22680, 22680, 22680, 4536 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The triangle of the corresponding numerators is A119947. The rationals appear in lowest terms.

The least common multiple (LCM) of row i gives [1, 4, 18, 48, 300, 360, 2940, 6720, 22680, ...], which coincides with A081528.

LINKS

Table of n, a(n) for n=1..42.

FORMULA

T(i,j) = denominator((A^2)[i,j]), where the lower triangular matrix A has elements a[i,j] = 1/i if j <= i, 0 if j > i.

EXAMPLE

The first rows of the table are:

  [1];

  [4, 4];

  [18, 18, 9];

  [48, 48, 48, 16];

  [300, 300, 300, 100, 25];

  [120, 120, 120, 360, 180, 36]; ...

PROG

(PARI) A119948_upto(n)={my(M=matrix(n, n, i, j, (j<=i)/i)^2); vector(n, r, apply(denominator, M[r, 1..r]))} \\ M. F. Hasler, Nov 05 2019

CROSSREFS

Row sums give A119950. Row sums of the triangle of rationals always give 1.

Sequence in context: A116561 A086448 A128090 * A005222 A214166 A214187

Adjacent sequences:  A119945 A119946 A119947 * A119949 A119950 A119951

KEYWORD

nonn,easy,frac,tabl

AUTHOR

Wolfdieter Lang, Jul 20 2006

EXTENSIONS

Edited by M. F. Hasler, Nov 05 2019

STATUS

approved

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Last modified May 9 09:58 EDT 2021. Contains 343713 sequences. (Running on oeis4.)