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A242592 Squarefree semiprimes, n=p*q, where reversal(n) is semiprime and reversal(n) = reversal(p)*reversal(q).

%I A242592 #8 May 19 2014 04:37:39
%S A242592 6,22,26,33,39,55,62,77,93,143,187,202,226,262,303,339,341,393,505,
%T A242592 622,626,707,781,933,939,1111,1177,1243,1313,1441,1469,1661,1717,1991,
%U A242592 2042,2062,2066,2206,2402,2426,2446,2462,2602,2642,3063,3093,3099,3131,3309
%N A242592 Squarefree semiprimes, n=p*q, where reversal(n) is semiprime and reversal(n) = reversal(p)*reversal(q).
%C A242592 Subsequence of A085751.
%H A242592 Michel Lagneau, <a href="/A242592/b242592.txt">Table of n, a(n) for n = 1..999</a>
%e A242592 1469 = 13*113 is in the sequence because reversal(1469) = 9641 = 31*311 where 31 = reversal(13) and 311 = reversal(113).
%p A242592 for n from 6 to 4000 do :
%p A242592   x:=factorset(n):n1:=nops(x):
%p A242592    if bigomega(n)= 2 and n1>1
%p A242592    then                 y:=convert(n,base,10):n2:=nops(y):p:=x[1]:q:=x[2]:xp1:=convert(p,base,10):nxp1:=nops(xp1):xq1:=convert(q,base,10):nxq1:=nops(xq1):sp:=sum('xp1[i]*10^(nxp1-i)', 'i'=1..nxp1):sq:=sum('xq1[i]*10^(nxq1-i)', 'i'=1..nxq1):lst:={sp} union {sq}:s:=sum('y[i]*10^(n2-i)', 'i'=1..n2):x1:=factorset(s):nn1:=nops(x1):
%p A242592     if bigomega(s)=2 and nn1>1
%p A242592     then
%p A242592     z:=convert(s,base,10):n3:=nops(z): p1:=x1[1]:q1:=x1[2]:
%p A242592     lst1:={p1} union  {q1}:s1:=sum('z[i]*10^(n3-i)','i'=1..n3):
%p A242592        if lst = lst1
%p A242592         then
%p A242592         printf(`%d, `,n):
%p A242592         else
%p A242592        fi:
%p A242592      fi:
%p A242592     fi:
%p A242592   od:
%Y A242592 Cf. A001358, A006881, A085751, A210616.
%K A242592 nonn,base
%O A242592 1,1
%A A242592 _Michel Lagneau_, May 18 2014