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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 * A329257 A173266 A342149 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 3 14:25 EDT 2023. Contains 363116 sequences. (Running on oeis4.)