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A210488 a(n) is the index of A210487 when the n-th prime appears for the first time. 1
3, 4, 2, 20, 60, 92, 246, 752, 1289, 2084, 3383 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

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.

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

CROSSREFS

Cf. A000040, A210487, A147971.

Sequence in context: A166074 A225475 A259334 * A244364 A218610 A260958

Adjacent sequences:  A210485 A210486 A210487 * A210489 A210490 A210491

KEYWORD

nonn,hard

AUTHOR

Lei Zhou, Jan 23 2013

STATUS

approved

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Last modified August 20 21:29 EDT 2019. Contains 326155 sequences. (Running on oeis4.)