OFFSET
1,2
COMMENTS
a(n) > 0 if and only if n+1 is in A046868. a(n) < 0 if and only if n+1 is in A233671. - Chai Wah Wu, Sep 10 2019
LINKS
Stefano Spezia, Table of n, a(n) for n = 1..10000
L. Panaitopol, On the sequence p(n)^2=p(n-1)*p(n+1), J. Inequal. Pure Appl. Math., Volume 3, Issue 4, Article 53, 2002.
FORMULA
a(n) = determinant of matrix
| prime(n+1) prime(n)|
| prime(n+2) prime(n+1)|. - Zak Seidov, Jul 23 2008, indices corrected by Gary Detlefs, Dec 09 2011
a(n) = 2*A342567(n+1) for n >= 2. - Hugo Pfoertner, Jun 20 2021
MAPLE
A056221 := proc(n)
ithprime(n+1)^2-ithprime(n)*ithprime(n+2) ;
end proc:
seq(A056221(n), n=1..10) ; # R. J. Mathar, Dec 10 2011
MATHEMATICA
a[n_]:=Prime[n+1]^2-Prime[n]Prime[n+2]; Array[a, 50] (* Stefano Spezia, Jul 15 2024 *)
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Aug 06 2000
STATUS
approved