The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A118772 Determinant of n X n matrix containing the first n^2 3-almost primes in increasing order. 3
 8, -56, 156, 13328, -920, -83678, 1261988, 54252742, 214409844, -3528354250, 247094703588, -509185323508, 15154985424718, 884710401396570, 49777180907707320, -172913218088289027, 844641410704177098, 3066058962037715903, -33948947842497666568 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 3-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 3-almost primes in increasing order, the second column contains the next n 3-almost primes in increasing order, etc. Equivalently, first row contains first n 3-almost primes in increasing order, second row contains next n 3-almost primes in increasing order, etc. See also: A118713 a(n) = semiprime circulant. LINKS EXAMPLE a(2) = -56 because of the determinant -56 = |8, 12| 18, 20|. a(6) = -83678 because of the determinant -83678 = | 8, 12, 18, 20, 27, 28| | 30, 42, 44, 45, 50, 52| | 63, 66, 68, 70, 75, 76| | 78, 92, 98, 99, 102, 105| | 110, 114, 116, 117, 124, 125| | 130, 138, 147, 148, 153, 154|. MATHEMATICA ThreeAlmostPrimePi[ n_ ] := Sum[ PrimePi[ n/(Prime @ i*Prime @ j) ] - j + 1, {i, PrimePi[ n^(1/3) ]}, {j, i, PrimePi@ Sqrt[ n/Prime @ i ]} ]; ThreeAlmostPrime[ n_ ] := Block[ {e = Floor[ Log[ 2, n ] + 1 ], a, b}, a = 2^e; Do[ b = 2^p; While[ ThreeAlmostPrimePi[ a ] < n, a = a + b ]; a = a - b/2, {p, e, 0, -1} ]; a + b/2 ]; Table[ Det[ Partition[ Array[ ThreeAlmostPrime, n^2 ], n ] ], {n, 19} ] (* Robert G. Wilson v, May 26 2006 *) With[{tap=Select[Range[4000], PrimeOmega[#]==3&]}, Table[Det[ Partition[ Take[tap, n^2], n]], {n, 20}]] (* Harvey P. Dale, Apr 17 2020 *) CROSSREFS Cf. A014612, A067276, A118713, A118770, A118779. Sequence in context: A160429 A003722 A044146 * A212817 A267522 A073831 Adjacent sequences:  A118769 A118770 A118771 * A118773 A118774 A118775 KEYWORD easy,sign AUTHOR Jonathan Vos Post, May 22 2006 EXTENSIONS More terms from Robert G. Wilson v, May 26 2006 Typos in Mma program corrected by Giovanni Resta, Jun 12 2016 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 8 13:26 EDT 2021. Contains 343666 sequences. (Running on oeis4.)