Annual Appeal: Please make a donation (tax deductible in USA) to keep the OEIS running. Over 5000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Cf. A063643 Primes p such that p+/-2 are semiprimes, A117328 Primes p such that p+/-4 are semiprimes.
Table of n, a(n) for n=1..55.
a(100)=571 because 571-2*100=371=7*53 (semiprime), 571+2*100=771=3*257 (semiprime).
Sequence in context: A157677 A092518 A110584 * A180538 A227217 A229176
Adjacent sequences: A115393 A115394 A115395 * A115397 A115398 A115399
Zak Seidov, Mar 08 2006