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 A264855 Integers n such that A002110(n)^2 - A002110(n) + 1 is prime. 0
 1, 2, 4, 5, 10, 14, 15, 20, 23, 46, 96, 281, 367, 542, 1380, 1395 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Initial primes of the form A002110(n)^2 - A002110(n) + 1 are 3, 31 and 43891. Intersection of this sequence and A014545 gives the values of n such that A002110(n)^3 + 1 is semiprime. LINKS EXAMPLE a(1) = 1 because 2^2 - 2 + 1 = 3 is prime. a(2) = 2 because 6^2 - 6 + 1 = 31 is prime. a(3) = 4 because 210^2 - 210 + 1 = 43891 is prime. MATHEMATICA Select[Range@ 400, PrimeQ[#^2 - # + 1 &@ Product[Prime@ k, {k, #}]] &] (* Michael De Vlieger, Nov 28 2015 *) PROG (PARI) a002110(n) = prod(k=1, n, prime(k)); for(n=0, 1e3, if(ispseudoprime(a002110(n)^2 - a002110(n) + 1), print1(n, ", "))) CROSSREFS Cf. A002110, A014545, A092061. Sequence in context: A018360 A133585 A218936 * A154318 A008283 A002237 Adjacent sequences:  A264852 A264853 A264854 * A264856 A264857 A264858 KEYWORD nonn,more AUTHOR Altug Alkan, Nov 26 2015 STATUS approved

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Last modified January 16 21:37 EST 2019. Contains 319206 sequences. (Running on oeis4.)