A227942 Semiprimes formed by inserting a semiprime between the semiprime's ordered factors.

393, 2105, 2147, 3155, 5255, 5357, 25829, 26231, 28241, 29447, 33913, 35719, 39331, 56513, 58517, 59519, 79113, 210653, 212261, 214271, 215879, 216683, 219497, 314147, 315953, 317759, 318361, 320167, 321973, 323779, 326789, 329197, 520541, 523547, 529559, 530561

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Chris K. Caldwell and G. L. Honaker, Jr., Prime Curio for 13361

Example

a(2)=2105 because the semiprime 10 inserted between its ordered prime factors (2 and 5) is a semiprime.

Prog

(PARI) issemi(n)=bigomega(n)==2
list(lim)=my(v=List(), t); forprime(q=2, sqrtint(lim\10), forprime(p=2, min(sqrtint(lim\q), q), t=eval(Str(p, p*q, q)); if(t>lim, next(2)); if(issemi(t), listput(v, t)))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Oct 04 2013

Crossrefs

Cf. A001358, A229480, A227943.

Sequence in context: A158002 A083752 A047825 * A201815 A201554 A172636

Adjacent sequences: A227939 A227940 A227941 * A227943 A227944 A227945

Keyword

nonn,base

Author

G. L. Honaker, Jr., Oct 03 2013

Extensions

More terms from Farideh Firoozbakht Oct 04 2013

Status

approved