

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
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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

Table of n, a(n) for n=1..16.


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



