OFFSET
1,1
COMMENTS
The only prime term is a(1) = 5.
All odd terms are of the form p^2-4.
All even terms are divisible by 8.
Numbers of the form (p^2-q^2)/8 (p, q odd primes, p>q) are listed in A124866.
Elliott & Richner call these "ans numbers". - Charles R Greathouse IV, Feb 17 2014
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
N. E. Elliott and D. Richner, An investigation of the set of ans numbers, Missouri J. of Math. Sci. 15 (2003), pp. 189-199.
Florian Luca, On the densities of some subsets of integers, Missouri Journal of Mathematical Sciences 19:3 (2007), pp. 167-170.
FORMULA
a(n) >> n log n, see Luca. - Charles R Greathouse IV, Feb 17 2014
MATHEMATICA
With[{nn=60}, Take[Union[#[[2]]^2-#[[1]]^2&/@Subsets[Prime[Range[nn]], {2}]], nn]] (* Harvey P. Dale, Aug 21 2015 *)
PROG
(PARI) is(n)=if(n%24, isprimepower(n+4)==2 || isprimepower(n+9)==2, fordiv(n/4, d, if(isprime(n/d/4+d) && isprime(n/d/4-d), return(1))); 0) \\ Charles R Greathouse IV, Feb 17 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Nov 10 2006
STATUS
approved