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A087112 Triangle in which the n-th row contains n distinct semiprimes not listed previously with all prime factors from among the first n primes. 12
4, 6, 9, 10, 15, 25, 14, 21, 35, 49, 22, 33, 55, 77, 121, 26, 39, 65, 91, 143, 169, 34, 51, 85, 119, 187, 221, 289, 38, 57, 95, 133, 209, 247, 323, 361, 46, 69, 115, 161, 253, 299, 391, 437, 529, 58, 87, 145, 203, 319, 377, 493, 551, 667, 841, 62, 93, 155, 217, 341, 403, 527, 589, 713, 899, 961 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Terms through row n, sorted, will provide terms for A077553 through row n*(n+1)/2.

LINKS

Reinhard Zumkeller, Rows n = 1..125 of triangle, flattened

FORMULA

The n-th row consists of n terms, prime(n)*prime(i), i=1..n.

T(n,k) = A000040(n) * A000040(k).

EXAMPLE

Triangle begins:

   4;

   6,   9;

  10,  15,  25;

  14,  21,  35,  49;

  22,  33,  55,  77, 121;

  26,  39,  65,  91, 143, 169;

MATHEMATICA

Table[ Prime[j]*Prime[k], {j, 11}, {k, j}] // Flatten (* Robert G. Wilson v, Feb 06 2017 *)

PROG

(Haskell)

a087112 n k = a087112_tabl !! (n-1) !! (k-1)

a087112_row n = map (* last ps) ps where ps = take n a000040_list

a087112_tabl = map a087112_row [1..]

-- Reinhard Zumkeller, Nov 25 2012

CROSSREFS

Cf. A100484 (left edge), A001248 (right edge), A143215 (row sums), A219603 (central terms of odd-indexed rows); A000040, A065342.

Sequence in context: A178378 A133234 A111206 * A077554 A262812 A287296

Adjacent sequences:  A087109 A087110 A087111 * A087113 A087114 A087115

KEYWORD

nonn,tabl

AUTHOR

Ray Chandler, Aug 21 2003

STATUS

approved

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Last modified July 10 02:05 EDT 2020. Contains 335570 sequences. (Running on oeis4.)