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%I #6 Mar 18 2014 05:41:31
%S 4,6,9,22,26,33,39,55,62,77,93,121,143,169,187,202,226,262,303,339,
%T 341,393,505,622,626,707,781,933,939,961,1111,1177,1243,1313,1441,
%U 1469,1661,1717,1991,2042,2062,2066,2206,2402,2426,2446,2462,2602,2642,3063,3093
%N Semiprimes n = p*q such that reverse(n)=reverse(p)*reverse(q) where reverse(n) is also semiprime.
%C Subsequence of A001358.
%H Giovanni Resta, <a href="/A239307/b239307.txt">Table of n, a(n) for n = 1..10000</a>
%e 1469 = 13*113 is in the sequence because reverse(1469)=reverse(13)*reverse(113) => 9641 = 31*311 where 31 and 311 are prime numbers.
%p with(numtheory):lst:={}:T1:=array(1..300):T2:=array(1..300):k:=0:
%p for n from 1 to 1000 do:
%p p:=ithprime(n):xp:=convert(p,base,10):
%p np:=nops(xp):sp:=sum('xp[np-i+1]*10^(i-1)','i'=1..np):
%p if type(sp,prime)=true
%p then
%p k:=k+1:T1[k]:=p:T2[k]:=sp:
%p else
%p fi:
%p od:
%p for i from 1 to k do:
%p for j from i to k do:
%p x:=T1[i]*T1[j]:y:=convert(x,base,10):n2:=nops(y):
%p s:=sum('y[n2-i+1]*10^(i-1)', 'i'=1..n2):
%p if T2[i]*T2[j]=s
%p then
%p lst:=lst union {x}:
%p else
%p fi:
%p od:
%p od:
%p print(lst):
%Y Cf. A007500, A001358.
%K nonn,base
%O 1,1
%A _Michel Lagneau_, Mar 15 2014
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