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A157188
Number of ways to write prime(n) as p*q-(p+q) with primes p<=q.
3
0, 2, 1, 1, 2, 0, 1, 1, 2, 1, 1, 0, 1, 1, 1, 0, 3, 0, 0, 4, 0, 1, 1, 0, 0, 1, 1, 2, 0, 0, 0, 2, 1, 1, 1, 0, 0, 1, 2, 0, 3, 0, 3, 0, 1, 1, 1, 1, 1, 0, 0, 3, 0, 2, 0, 2, 1, 1, 0, 1, 0, 0, 0, 4, 0, 0, 1, 0, 2, 0, 0, 4, 0, 0, 1, 2, 0, 0, 0, 0, 4, 0, 4, 0, 0, 1, 0, 0, 1, 1, 1, 3, 0, 1, 1, 3, 0, 1, 1, 0, 0, 0, 1, 1, 0
OFFSET
1,2
COMMENTS
Records in this sequence are given in A157189, the corresponding primes in A157190.
EXAMPLE
a(1)=0 since prime(1) = 2 cannot be written as pq-(p+q) for primes p,q.
a(2)=2 since prime(2) = 3 = 2*5-(2+5) = 3*3-(3+3) are the two possibilities.
PROG
(PARI) A157188(n)={ local(c=0, L=sqrtint(n=prime(n)+1)); fordiv( n, d, d>L&break; isprime(d+1) | next; isprime(n/d+1) & c++); c}
CROSSREFS
KEYWORD
nonn
AUTHOR
M. F. Hasler, Mar 11 2009
STATUS
approved