A387895 a(n) is the permanent of the n X n matrix containing the first n^2 semiprimes in increasing order.

1, 4, 94, 10736, 3419400, 2585633460, 3698719264041, 9230764410478364, 35173188742181847797, 193393712813174251699623, 1550699768728271062826693582, 16776240103135043263611146467522, 242100630777748565239412582808398530, 4528096627860706892634271952056347037210

Offset

0,2

Links

Table of n, a(n) for n=0..13.

Example

a(6) = 3698719264041:
  [ 4,  6,  9, 10,  14,  15]
  [21, 22, 25, 26,  33,  34]
  [35, 38, 39, 46,  49,  51]
  [55, 57, 58, 62,  65,  69]
  [74, 77, 82, 85,  86,  87]
  [91, 93, 94, 95, 106, 111]

Mathematica

SemiPrimePi[ n_ ] := Sum[ PrimePi[ n/Prime @ i ] - i + 1, {i, PrimePi @ Sqrt @ n} ]; SemiPrime[ n_ ] := Block[ {e = Floor[ Log[ 2, n ] + 1 ], a, b}, a = 2^e; Do[ b = 2^p; While[ SemiPrimePi[ a ] < n, a = a + b ]; a = a - b/2, {p, e, 0, -1} ]; a + b/2 ]; a[n_]:=Permanent[ Partition[ Array[ SemiPrime, n^2 ], n ] ]; Join[{1}, Array[a, 13]] (* after A118770 *)

Crossrefs

Cf. A114533, A118770, A387894.

Sequence in context: A220374 A220429 A210857 * A220682 A210926 A302121

Adjacent sequences: A387892 A387893 A387894 * A387896 A387897 A387898

Keyword

nonn

Author

Stefano Spezia, Sep 11 2025

Status

approved