A132288 Odd palindromes which are semiprimes with an even number of digits.

33, 55, 77, 1111, 1441, 1661, 1991, 3113, 3223, 3443, 3883, 7117, 7447, 7997, 9119, 9229, 9449, 100001, 103301, 104401, 107701, 113311, 115511, 116611, 124421, 125521, 130031, 136631, 139931, 146641, 152251, 157751, 160061, 163361, 164461, 169961, 170071

Offset: 1

Author

Artur Jasinski, Aug 16 2007

Keywords

• base
• nonn

Comments

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

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Intersection of A132285 and A001358.

Cf. A132286, A132287.

Programs

Maple

rev:= proc(n) local L,i; L:= convert(n,base,10); add(L[-i]*10^(i-1),i=1..nops(L)) end proc:
f:= proc(m) local A,i,j,k;
  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])])
end proc:
seq(op(f(m)),m=2..6,2); # Robert Israel, Jan 05 2025

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

Formula

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

Extensions

More terms from Michel Marcus, Nov 05 2013

Name edited by Robert Israel, Jan 05 2025