A357934 Products of two distinct lesser twin primes A001359.

15, 33, 51, 55, 85, 87, 123, 145, 177, 187, 205, 213, 295, 303, 319, 321, 355, 411, 447, 451, 493, 505, 535, 537, 573, 591, 649, 681, 685, 697, 717, 745, 781, 807, 843, 895, 933, 955, 985, 1003, 1041, 1111, 1135, 1177, 1189, 1195, 1207, 1257, 1293, 1345, 1383, 1405, 1507, 1555, 1563

Offset

1,1

Links

R. J. Mathar, Table of n, a(n) for n = 1..10000

Maple

omega := proc(n)
    nops(numtheory[factorset](n)) ;
end proc:
isA357934 := proc(n)
    local pe, p, q;
    if numtheory[bigomega](n)= 2 and omega(n) =2 then
        pe := ifactors(n)[2] ;
        p := op(1, op(1, pe)) ;
        q := op(1, op(2, pe)) ;
        if isprime(p+2) and isprime(q+2) then
            true;
        else
            false;
        end if;
    else
        false;
    end if;
end proc:
for n from 10 to 2000 do
    if isA357934(n) then
        printf("%d, ", n) ;
    end if;
end do: # R. J. Mathar, Feb 13 2025

Mathematica

d = {}; less = Select[Range[1607], PrimeQ[#] && PrimeQ[# + 2] &]; Do[Do[AppendTo[d, less[[m]] less[[n]]], {m, n + 1, Length[less]}], {n,
  1, Length[less] - 1}]; Take[Sort[d], 55]

Prog

(PARI) list(lim)=my(v=List(), p=5); forprime(q=7, lim\3+2, if(q-p==2, my(r=3); forprime(s=5, min(lim\p+2, p), if(s-r==2, listput(v, p*r)); r=s)); p=q); Set(v) \\ Charles R Greathouse IV, Oct 21 2022

Crossrefs

Cf. A001359. Subsequence of A006881.

Sequence in context: A351562 A316153 A190754 * A327900 A071965 A242677

Adjacent sequences: A357931 A357932 A357933 * A357935 A357936 A357937

Keyword

nonn

Author

Artur Jasinski, Oct 21 2022

Status

approved