A085751 Semiprimes whose reversal is also a semiprime.

4, 6, 9, 15, 22, 26, 33, 39, 49, 51, 55, 58, 62, 77, 85, 93, 94, 111, 115, 121, 122, 123, 129, 141, 143, 155, 158, 159, 161, 169, 177, 178, 183, 185, 187, 202, 203, 205, 221, 226, 262, 265, 289, 302, 303, 314, 319, 321, 323, 326, 327, 329, 335, 339, 341, 355

Offset: 1

Author

Jason Earls, Jul 21 2003

Keywords

• base
• easy
• nonn

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A001358, A097393.

Programs

Mathematica

Select[Range[400],PrimeOmega[#]==PrimeOmega[IntegerReverse[#]]==2&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 09 2016 *)

PARI

rev(n)=subst(Polrev(digits(n)), 'x, 10)
issemi(n)=bigomega(n)==2
list(lim)=my(v=List()); forprime(p=2, lim\2, forprime(q=2, min(lim\p, p), if(issemi(rev(p*q)), listput(v, p*q)))); Set(v) \\ Charles R Greathouse IV, Jan 27 2015