A103655 Indices of primes which are the average of two successive semiprimes.

3, 16, 19, 24, 30, 32, 40, 47, 54, 62, 63, 68, 75, 80, 87, 93, 94, 95, 115, 124, 126, 129, 133, 136, 138, 157, 160, 162, 167, 169, 175, 177, 179, 187, 196, 205, 222, 232, 233, 239, 240, 247, 258, 265, 267, 270, 274, 277, 279, 298, 299, 318, 327, 335, 336, 339

Offset

1,1

Links

Zak Seidov, Table of n, a(n) for n = 1..10000

Formula

a(n)=pi(A103654(n)).

Example

19 is a member because p(19)=67; 65 and 69 are two successive semiprimes closest to 67 and 67=(65+69)/2.

Mathematica

PrimePi[#]&/@Select[Mean/@Partition[Select[Range[2500], PrimeOmega[#]==2&], 2, 1], PrimeQ] (* Harvey P. Dale, Sep 08 2024 *)

Crossrefs

Corresponding primes: A103654. Primes: A000040, semiprimes: A001358, number of primes between two successive semiprimes: A088700, number of semiprimes between two successive primes: A103668.

Cf. A000040, A088700, A103654, A001358, A103668, A103669.

Sequence in context: A068516 A219508 A032922 * A022126 A127006 A042075

Adjacent sequences: A103652 A103653 A103654 * A103656 A103657 A103658

Keyword

nonn

Author

Zak Seidov, Feb 12 2005

Status

approved