A285804 Composite numbers of the form 12*k+5 or 12*k+7 for some k.

55, 65, 77, 91, 115, 125, 161, 175, 185, 187, 209, 221, 235, 245, 247, 259, 295, 305, 319, 329, 341, 343, 355, 365, 377, 391, 403, 413, 415, 425, 427, 437, 451, 473, 475, 485, 497, 511, 533, 535, 545, 559, 581, 583, 595, 605, 629, 655, 665

Offset

1,1

Comments

Conjecture: Let r(n) = (a(n)-1)/(a(n)+1) if a(n) mod 4 = 1, (a(n)+1)/(a(n)-1) otherwise; then Product_{n>=1} r(n) = (28/27) * (32/33) * (38/39) * (46/45) * ... = 1.

Links

Table of n, a(n) for n=1..49.

Maple

remove(isprime, [seq(seq(12*k+j, j=[5, 7]), k=1..100)]); # Robert Israel, Apr 28 2017

Prog

(PARI) {
for(n=0, 100,
    n12=12*n; n5=n12+5; n7=n12+7;
    if(!isprime(n5), print1(n5", "));
    if(!isprime(n7), print1(n7", "))
   )
}

Crossrefs

Sequence in context: A039356 A043179 A043959 * A269808 A004434 A168109

Adjacent sequences: A285801 A285802 A285803 * A285805 A285806 A285807

Keyword

nonn

Author

Dimitris Valianatos, Apr 26 2017

Status

approved