A157188 - OEIS

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A157188

Number of ways to write prime(n) as p*q-(p+q) with primes p<=q.

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; internal format)

	OFFSET	`1,2`
	COMMENTS	`Records in this sequence are given in A157189, the corresponding primes in A157190.`
	LINKS	`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 = 25-(2+5) = 33-(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: A025925 A109066 A079066 * A173266 A096496 A117209` `Adjacent sequences: A157185 A157186 A157187 * A157189 A157190 A157191`
	KEYWORD	`nonn`
	AUTHOR	`M. F. Hasler (www.univ-ag.fr/~mhasler), Mar 11 2009`

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Last modified February 14 04:29 EST 2012. Contains 205570 sequences.