OFFSET
1,1
FORMULA
a(n) = | p(n)*p(n+2) - p(n+1)*p(n+3) | +1
EXAMPLE
7, 11, 13, 17 --> | 7*13-11*17 | + 1 = 97
19, 23, 29, 31 --> | 19*29 - 23*31 | + 1 = 163
MAPLE
P:=proc(n) local i, j; for i from 1 by 1 to n do j:=abs(ithprime(i)*ithprime(i+2)-ithprime(i+1)*ithprime(i+3))+1; if isprime(j) then print(j); fi; od; end: P(1000);
MATHEMATICA
Select[Abs[#[[1]]#[[3]]-#[[2]]#[[4]]]+1&/@Partition[ Prime[ Range[ 200]], 4, 1], PrimeQ] (* Harvey P. Dale, Oct 01 2015 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, May 02 2006
STATUS
approved