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 A118779 Determinant of n X n matrix containing the first n^2 4-almost primes in increasing order. 3
 16, -224, 0, 182016, 12734992, -80430368, -125120640, 1334967760, 1060202222660, -2759409121760, 54820105989504, -14148083510835712, 49989643415528010, 299304923505836144, 1713123391839442498, 93227182153040103540, -86403659709730762670 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 4-almost prime analog of A067276 Determinant of n X n matrix containing the first n^2 primes in increasing order. The first column contains the first n 4-almost primes (A014613) in increasing order, the second column contains the next n 4-almost primes in increasing order, etc. Equivalently, first row contains first n 4-almost primes in increasing order, second row contains next n 4-almost primes in increasing order, etc. See also: A118713 a(n) = semiprime circulant. LINKS EXAMPLE a(2) = -224 because of the determinant -224 = |16, 24| |36, 40|. a(3) = 0 because this matrix is singular: 0 = |16, 24, 36| |40, 54, 56| |60, 81, 84|. a(6) = -80430368 because of the determinant -80430368 = | 16, 24, 36, 40, 54, 56| | 60, 81, 84, 88, 90, 100| | 104, 126, 132, 135, 136, 140| | 150, 152, 156, 184, 189, 196| | 198, 204, 210, 220, 225, 228| | 232, 234, 248, 250, 260, 276|. a(8) = 1334967760 = | 16, 24, 36, 40, 54, 56, 60, 81| | 84, 88, 90, 100, 104, 126, 132, 135| |136, 140, 150, 152, 156, 184, 189, 196| |198, 204, 210, 220, 225, 228, 232, 234| |248, 250, 260, 276, 294, 296, 297, 306| |308, 315, 328, 330, 340, 342, 344, 348| |350, 351, 364, 372, 375, 376, 380, 390| |414, 424, 441, 444, 459, 460, 462, 472|. MATHEMATICA FourAlmostPrimePi[n_] := Sum[PrimePi[n/(Prime@i*Prime@j*Prime@k)] - k + 1, {i, PrimePi[n^(1/4)]}, {j, i, PrimePi[(n/Prime@i)^(1/3)]}, {k, j, PrimePi@Sqrt[n/(Prime@i*Prime@j)]}]; FourAlmostPrime[n_] := Block[{e = Floor[Log[2, n] + 1], a, b}, a = 2^e; Do[b = 2^p; While[FourAlmostPrimePi[a] < n, a = a + b]; a = a - b/2, {p, e, 0, -1}]; a + b/2]; Table[Det[Partition[Array[FourAlmostPrime, n^2], n]], {n, 17}] (* Robert G. Wilson v, May 26 2006 *) CROSSREFS Cf. A014613, A118713, A067276, A118770, A118772. Sequence in context: A092657 A078266 A093746 * A209444 A051822 A017438 Adjacent sequences:  A118776 A118777 A118778 * A118780 A118781 A118782 KEYWORD easy,sign AUTHOR Jonathan Vos Post, May 22 2006 EXTENSIONS More terms from Robert G. Wilson v, May 26 2006 STATUS approved

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Last modified June 2 10:12 EDT 2020. Contains 334769 sequences. (Running on oeis4.)