OFFSET
1,1
COMMENTS
Number n is in the sequence if and only if the following seven numbers are all composite:
P_1(n) = 2n^4 + 4n^3 + 6n^2 + 4n + 1,
P_2(n) = 3n^4 + 12n^3 + 30n^2 + 36n + 17,
P_3(n) = 5n^4 + 40n^3 + 180n^2 + 400n + 354,
P_4(n) = 6n^4 + 60n^3 + 330n^2 + 900n + 979,
P_5(n) = 10n^4 + 180n^3 + 1710n^2 + 8100n + 15333,
P_6(n) = 15n^4 + 420n^3 + 6090n^2 + 44100n + 127687,
P_7(n) = 30n^4 + 1740n^3 + 51330n^2 + 756900n + 4463999.
For a generalization, see comment in A256581.
LINKS
Peter J. C. Moses, Table of n, a(n) for n = 1..1000
PROG
(Magma) [n: n in [0..2*10^2] | not IsPrime(2*n^4+4*n^3+6*n^2 +4*n+1) and not IsPrime(3*n^4+12*n^3+30*n^2+36*n+17) and not IsPrime(5*n^4+40*n^3+180*n^2+400*n+354) and not IsPrime(6*n^4+60*n^3+330*n^2+900*n+979) and not IsPrime(10*n^4+ 180*n^3+1710*n^2+8100*n+15333) and not IsPrime(15*n^4+ 420*n^3+6090*n^2+44100*n+127687) and not IsPrime(30*n^4+ 1740*n^3+51330*n^2+756900*n+4463999)]; // Vincenzo Librandi, Apr 03 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev and Peter J. C. Moses, Apr 01 2015
STATUS
approved