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Odd palindromes which are semiprimes with an even number of digits.
2

%I #20 Jan 06 2025 04:13:47

%S 33,55,77,1111,1441,1661,1991,3113,3223,3443,3883,7117,7447,7997,9119,

%T 9229,9449,100001,103301,104401,107701,113311,115511,116611,124421,

%U 125521,130031,136631,139931,146641,152251,157751,160061,163361,164461,169961,170071

%N Odd palindromes which are semiprimes with an even number of digits.

%C One of the divisors is 11 and the other is A132287(n).

%H Robert Israel, <a href="/A132288/b132288.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = 11*A132287(n).

%p rev:= proc(n) local L,i; L:= convert(n,base,10); add(L[-i]*10^(i-1),i=1..nops(L)) end proc:

%p f:= proc(m) local A,i,j,k;

%p select(t -> isprime(t/11), [seq(seq(10^(m-1)*i + 10^(m/2)*j + rev(10^(m/2-1)*i+j),j=0 .. 10^(m/2-1)-1),i=[1,3,5,7, 9])])

%p end proc:

%p seq(op(f(m)),m=2..6,2); # _Robert Israel_, Jan 05 2025

%o (PARI) lista(nn) = {for(n=1, nn, if (ismo(n) && (bigomega(n) == 2), print1(n, ", ");););} \\ where ismo is isok in A132285 \\ _Michel Marcus_, Nov 05 2013

%Y Intersection of A132285 and A001358.

%Y Cf. A132286, A132287.

%K base,nonn

%O 1,1

%A _Artur Jasinski_, Aug 16 2007

%E More terms from _Michel Marcus_, Nov 05 2013

%E Name edited by _Robert Israel_, Jan 05 2025