cp's OEIS Frontend

A083815 Semiprimes whose prime factors are distinct and the reversal of one factor is equal to the other.

%I A083815 #17 Dec 26 2018 21:35:30
%S A083815 403,1207,2701,7663,35143,75007,117907,127087,140209,173809,197209,
%T A083815 247021,257821,342127,382387,643063,692443,743623,1226221,1341331,
%U A083815 1626151,1698661,1739161,2073991,2138791,2528611,2561011,3321133
%N A083815 Semiprimes whose prime factors are distinct and the reversal of one factor is equal to the other.
%C A083815 Products of emirp pairs, sorted. - _Lekraj Beedassy_, Jan 10 2008
%H A083815 Robert Israel, <a href="/A083815/b083815.txt">Table of n, a(n) for n = 1..10000</a>
%e A083815 a(2)= 1207 = 17 * 71.
%p A083815 revdigs:= proc(n) local i,L;
%p A083815   L:= convert(n,base,10);
%p A083815   add(L[-i]*10^(i-1),i=1..nops(L))
%p A083815 end proc:
%p A083815 f:= proc(p) local r;
%p A083815   if not isprime(p) then return NULL fi;
%p A083815   r:= revdigs(p);
%p A083815   if r > p and isprime(r) then r*p fi
%p A083815 end proc:
%p A083815 sort(map(f, [seq(i,i=13..9999,2)])); # _Robert Israel_, Dec 26 2018
%Y A083815 Cf. A001358, A006567, A109308.
%K A083815 base,nonn
%O A083815 1,1
%A A083815 _Jason Earls_, Jun 17 2003
%E A083815 More terms from _Ray Chandler_, Jul 22 2003