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A338905
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Irregular triangle read by rows where row n lists all squarefree semiprimes with prime indices summing to n.
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14
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6, 10, 14, 15, 21, 22, 26, 33, 35, 34, 39, 55, 38, 51, 65, 77, 46, 57, 85, 91, 58, 69, 95, 119, 143, 62, 87, 115, 133, 187, 74, 93, 145, 161, 209, 221, 82, 111, 155, 203, 247, 253, 86, 123, 185, 217, 299, 319, 323, 94, 129, 205, 259, 341, 377, 391, 106, 141
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OFFSET
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3,1
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COMMENTS
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A squarefree semiprime is a product of any two distinct prime numbers. A prime index of n is a number m such that the m-th prime number divides n. The multiset of prime indices of n is row n of A112798.
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LINKS
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EXAMPLE
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Triangle begins:
6
10
14 15
21 22
26 33 35
34 39 55
38 51 65 77
46 57 85 91
58 69 95 119 143
62 87 115 133 187
74 93 145 161 209 221
82 111 155 203 247 253
86 123 185 217 299 319 323
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MATHEMATICA
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Table[Sort[Table[Prime[k]*Prime[n-k], {k, (n-1)/2}]], {n, 3, 10}]
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CROSSREFS
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A004526 (shifted right) gives row lengths.
A025129 (shifted right) gives row sums.
A056239 gives sum of prime indices (Heinz weight).
A339116 is a different triangle whose diagonals are these rows.
A338904 is the not necessarily squarefree version, with row sums A024697.
A087112 groups semiprimes by greater factor.
A168472 gives partial sums of squarefree semiprimes.
Cf. A000040, A001221, A014342, A098350, A112798, A320656, A338901, A338906, A339003, A339004, A339005, A339115.
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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