login
A351336
Odd pseudoprimes to base 3; composite terms of A271116.
0
91, 121, 671, 703, 949, 1105, 1541, 1729, 1891, 2465, 2665, 2701, 2821, 3281, 3367, 3751, 4961, 5551, 6601, 7381, 8401, 8911, 10585, 11011, 12403, 14383, 15203, 15457, 15841, 16471, 16531, 18721, 19345, 23521, 24661, 24727, 28009, 29161, 29341, 30857, 31621
OFFSET
1,1
COMMENTS
Only 2760 of the first 10 million terms of A271116 are nonprimes (0.03%). These composite terms are heavily skewed to rightmost digit = 1.
These odd composites all appear in A005935 (A005935 having an additional 27 terms (all parity 0) through the same term = 179146207).
MATHEMATICA
q[n_] := CompositeQ[n] && Divisible[Round[3^n/12], n]; Select[Range[32000], q] (* Amiram Eldar, Feb 09 2022 *)
PROG
(PARI) is(n) = (n>1) && !isprime(n) && (lift(Mod(3, 4*n)^(n-1))==1); \\ Michel Marcus, Feb 09 2022; after A271116
(PARI) list(lim)=my(v=List()); forcomposite(n=91, lim\1, if(bittest(34, n%6) && Mod(3, n)^(n-1)==1, listput(v, n))); Vec(v) \\ Charles R Greathouse IV, Feb 09 2022
CROSSREFS
Intersection of A002808 and A271116; intersection of A005935 and A005408; subsequence of A038509.
Sequence in context: A092125 A005935 A020307 * A328662 A020235 A046427
KEYWORD
nonn
AUTHOR
Bill McEachen, Feb 07 2022
STATUS
approved