A143235 Triangle read by rows: T(n,k) = tau(n)*tau(k), the product of the number of divisors.

1, 2, 4, 2, 4, 4, 3, 6, 6, 9, 2, 4, 4, 6, 4, 4, 8, 8, 12, 8, 16, 2, 4, 4, 6, 4, 8, 4, 4, 8, 8, 12, 8, 16, 8, 16, 3, 6, 6, 9, 6, 12, 6, 12, 9, 4, 8, 8, 12, 8, 16, 8, 16, 12, 16, 2, 4, 4, 6, 4, 8, 4, 8, 6, 8, 4, 6, 12, 12, 18, 12, 24, 12, 24, 18, 24, 12, 36, 2, 4, 4, 6, 4, 8, 4, 8, 6, 8, 4, 12, 4

Offset

1,2

Comments

The triangle can also be created by the triple matrix product A130209 * A000012 * A130209.

Links

Table of n, a(n) for n=1..91.

Formula

T(n,k) = A000005(n)*A000005(k), 1<=k<=n.

Example

First few rows of the triangle =
1;
2, 4;
2, 4, 4;
3, 6, 6, 9;
2, 4, 4, 6, 4;
4, 8, 8, 12, 8, 16;
2, 4, 4, 6, 4, 8, 4;
4, 8, 8, 12, 8, 16, 8, 16;
3, 6, 6, 9, 6, 12, 6, 12, 9;
...
T(9,6) = 12 = d(9)*d(6) = 3*4.

Crossrefs

Cf. A000005, A143236 (row sums).

Sequence in context: A004020 A363290 A246436 * A069465 A047947 A018838

Adjacent sequences: A143232 A143233 A143234 * A143236 A143237 A143238

Keyword

nonn,tabl,easy

Author

Gary W. Adamson, Aug 01 2008

Status

approved