A083815 - OEIS

%I #17 Dec 26 2018 21:35:30

%S 403,1207,2701,7663,35143,75007,117907,127087,140209,173809,197209,

%T 247021,257821,342127,382387,643063,692443,743623,1226221,1341331,

%U 1626151,1698661,1739161,2073991,2138791,2528611,2561011,3321133

%N Semiprimes whose prime factors are distinct and the reversal of one factor is equal to the other.

%C Products of emirp pairs, sorted. - _Lekraj Beedassy_, Jan 10 2008

%H Robert Israel, <a href="/A083815/b083815.txt">Table of n, a(n) for n = 1..10000</a>

%e a(2)= 1207 = 17 * 71.

%p revdigs:= proc(n) local i,L;

%p   L:= convert(n,base,10);

%p   add(L[-i]*10^(i-1),i=1..nops(L))

%p end proc:

%p f:= proc(p) local r;

%p   if not isprime(p) then return NULL fi;

%p   r:= revdigs(p);

%p   if r > p and isprime(r) then r*p fi

%p end proc:

%p sort(map(f, [seq(i,i=13..9999,2)])); # _Robert Israel_, Dec 26 2018

%Y Cf. A001358, A006567, A109308.

%K base,nonn

%O 1,1

%A _Jason Earls_, Jun 17 2003

%E More terms from _Ray Chandler_, Jul 22 2003