A210488 a(n) is the index of A210487 when the n-th prime appears for the first time.

3, 4, 2, 20, 60, 92, 246, 752, 1289, 2084, 3383

Offset: 1

Author

Lei Zhou, Jan 23 2013

Keywords

• nonn
• hard

Examples

			In A210487, 2 appears for the first time as A210487(3), so a(1)=3;
3 appears for the first time as A210487(4), so a(2)=4;
5 appears for the first time as A210487(2), so a(3)=2.
		

Crossrefs

Cf. A000040, A210487, A147971.

Programs

Maple

N := 60 ;
A210488 := [seq(0,i=1..N)] ;
for n from 2 do
    a := A210487(n) ;
    if isprime(a) then
        idx := numtheory[pi](a) ;
        if idx <= N then
        if op(idx,A210488) = 0 then
            A210488  := subsop(idx=n,A210488) ;
            print(A210488) ;
        end if;
        end if;
    end if;
end do: # R. J. Mathar, Apr 17 2013

Mathematica

nn = 11; a = Table[0, {nn}]; k = 1; While[Times @@ a == 0, k++; p1 = Prime[k]; id = PrimePi[Min[Table[Last[FactorInteger[Prime[k]^2 - Prime[j]^2]][[1]], {j, k - 1}]]]; If[id <= nn && a[[id]] == 0, a[[id]] = k]]; a