OFFSET
1,2
EXAMPLE
a(1)=1 because there are no primes in the interval (1^2-1, 1^2) = (0, 1) and no primes in the interval (1^2, 1^2+1) = (1, 2).
a(2)=2 because there is 1 prime in the interval (2^2-2, 2^2) = (2, 4) and one prime in the interval (2^2, 2^2+2) = (4, 6).
MAPLE
isA192391 := proc(n) numtheory[pi](n^2-1)-numtheory[pi](n^2-n) = numtheory[pi](n^2+n-1)-numtheory[pi](n^2-1) ; end proc:
for n from 1 to 600 do if isA192391(n) then printf("%d, ", n); end if; end do: # R. J. Mathar, Jul 08 2011
MATHEMATICA
Select[Range[500], PrimePi[#^2] - PrimePi[#^2 - #] == PrimePi[#^2 + #] - PrimePi[#^2] &] (* Alonso del Arte, Jun 29 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Jun 29 2011
EXTENSIONS
32 inserted and a few terms beyond 51 added by Alonso del Arte, Jun 29 2011
STATUS
approved