

A224980


Number of primes of the form pq1 where q is any prime < p = prime(n).


1



0, 0, 1, 1, 3, 2, 4, 4, 5, 4, 6, 8, 6, 8, 7, 6, 7, 12, 12, 10, 12, 14, 9, 8, 14, 12, 16, 11, 16, 14, 20, 14, 10, 16, 10, 24, 22, 20, 11, 12, 13, 28, 16, 22, 18, 26, 38, 22, 13, 24, 14, 18, 36, 18, 16, 17, 18, 38, 32, 28, 32, 16, 30, 24, 34, 20, 48, 38, 17
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OFFSET

1,5


LINKS

Table of n, a(n) for n=1..69.


EXAMPLE

For n=5, p=11, there are a(5)=3 solutions: 1131=7, 1151=5, and 1171=3.


MATHEMATICA

Table[p = Prime[n]; c = 0; i = 1; While[i < n, If[PrimeQ[p  Prime[i]  1], c = c + 1]; i++]; c, {n, 69}]


PROG

(PARI) a(n)=my(p=prime(n), s); forprime(q=2, p1, s+=isprime(pq1)); s \\ Charles R Greathouse IV, Apr 22 2013


CROSSREFS

Cf. A224748, A224908.
Sequence in context: A321232 A326015 A078822 * A154392 A069745 A112199
Adjacent sequences: A224977 A224978 A224979 * A224981 A224982 A224983


KEYWORD

nonn


AUTHOR

Jayanta Basu, Apr 22 2013


STATUS

approved



