A398488 - OEIS

A398488

Number of primes between the n-th odd semiprime and the following odd semiprime.

2, 2, 1, 2, 0, 1, 3, 0, 1, 0, 2, 1, 2, 2, 0, 1, 0, 0, 5, 1, 0, 0, 0, 1, 1, 2, 0, 0, 2, 1, 0, 2, 1, 2, 0, 0, 4, 0, 0, 0, 1, 0, 0, 0, 0, 4, 0, 2, 0, 1, 1, 1, 0, 5, 0, 0, 1, 0, 0, 0, 0, 1, 3, 0, 0, 0, 0, 1, 1, 0, 3, 1, 0, 1, 1, 1, 2, 0, 0, 2

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..80.

FORMULA

a(n) = A000720(A046315(n+1)) - A000720(A046315(n)).

EXAMPLE

a(1) = 2 because the 1st and 2nd odd semiprimes are 9 and 15, and there are exactly 2 primes strictly between them (11 and 13).

a(5) = 0 because the 5th and 6th odd semiprimes are 33 and 35, and there are no primes between them.

CROSSREFS

Cf. A001358, A046315, A000720, A000040.

Sequence in context: A145783 A145785 A094022 * A134177 A190615 A129402

Adjacent sequences: A398485 A398486 A398487 * A398489 A398490 A398491

KEYWORD

nonn

AUTHOR

Michael Shmoish, Jul 31 2026

STATUS

approved