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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Records in this sequence are given in A157189, the corresponding primes in A157190.

LINKS

Table of n, a(n) for n=1..105.

C. Rivera (Ed.), Puzzle 482: Two Bergot questions, March 2009.

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

Cf. A157187-A157190

Sequence in context: A240857 A109066 A079066 * A173266 A224326 A096496

Adjacent sequences:  A157185 A157186 A157187 * A157189 A157190 A157191

KEYWORD

nonn

AUTHOR

M. F. Hasler, Mar 11 2009

STATUS

approved

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Last modified June 19 13:11 EDT 2019. Contains 324222 sequences. (Running on oeis4.)