A113519 Semiprimes in A056105.

9, 22, 134, 177, 226, 482, 737, 1046, 1282, 1681, 1977, 2641, 3202, 3401, 3817, 4034, 4486, 5462, 5721, 6817, 7401, 7702, 8966, 9634, 9977, 10681, 11042, 11409, 12937, 15409, 16726, 17177, 18566, 21506, 28617, 29801

Offset

1,1

Comments

Intersection of A056105 and A001358.

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Example

A056105(44) = 3*44^2 - 2*44 + 1 = 5721 = 3 * 1907 which is a semiprime.
A056105(24) = 3*24^2 - 2*24 + 1 = 1681 = 41^2 which is a semiprime (the two prime factors need not be distinct).
A056105(100) = 3*100^2 - 2*100 + 1 = 29801 = 17 * 1753, which is a semiprime.

Maple

for n from 0 to 300 do
    s := 3*n^2-2*n+1 ;
    if isA001358(s) then
        printf("%d, ", s) ;
    end if;
end do: # R. J. Mathar, Jun 30 2020

Mathematica

Select[Array[3 #^2 - 2 # + 1 &, 100], PrimeOmega[#] == 2 &] (* Michael De Vlieger, Mar 17 2021 *)

Crossrefs

Cf. A001358, A056105.

Cf. A113524, A113525, A113527, A113528, A113530.

Sequence in context: A232024 A327150 A264651 * A300462 A123833 A156342

Adjacent sequences: A113516 A113517 A113518 * A113520 A113521 A113522

Keyword

easy,nonn

Author

Jonathan Vos Post, Jan 12 2006

Status

approved