OFFSET
1,1
COMMENTS
Composites analog of A117301 Determinants of 2 X 2 matrices of continuous blocks of 4 consecutive primes. See also: A118780 Determinants of 2 X 2 matrices of continuous blocks of 4 consecutive semiprimes. The terminology "continuous" is used to distinguish from "discrete" which would be (in this composites case) block 1: 4, 6, 8, 9; block 2: 10, 12, 14, 15 and so forth. It is not until a(12) that we break the pattern of a(2n)=a(2n-1); there seem to be strangely many such pairs of two identical values. a(12) is also the first odd value in the sequence and the first prime.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
a(1) = -12 =
|4 6|
|8 9|.
MATHEMATICA
Module[{nn=100, cmps}, cmps=Select[Range[nn], CompositeQ]; Det[ ArrayReshape[ #, {2, 2}]]&/@Table[Take[cmps, {n, n+3}], {n, Length[cmps]-3}]] (* Harvey P. Dale, Aug 03 2020 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Jonathan Vos Post, May 24 2006
STATUS
approved