login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A085751 Semiprimes whose reversal is also a semiprime. 9

%I #12 Dec 15 2017 17:36:28

%S 4,6,9,15,22,26,33,39,49,51,55,58,62,77,85,93,94,111,115,121,122,123,

%T 129,141,143,155,158,159,161,169,177,178,183,185,187,202,203,205,221,

%U 226,262,265,289,302,303,314,319,321,323,326,327,329,335,339,341,355

%N Semiprimes whose reversal is also a semiprime.

%H T. D. Noe, <a href="/A085751/b085751.txt">Table of n, a(n) for n = 1..1000</a>

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

%o (PARI) rev(n)=subst(Polrev(digits(n)), 'x, 10)

%o issemi(n)=bigomega(n)==2

%o 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

%Y Cf. A001358, A097393.

%K base,easy,nonn

%O 1,1

%A _Jason Earls_, Jul 21 2003

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 29 08:13 EDT 2024. Contains 371265 sequences. (Running on oeis4.)