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

1,1

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

Formula

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

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

Prog

(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

Crossrefs

Intersection of A132285 and A001358.

Cf. A132286, A132287.

Sequence in context: A024628 A061864 A075810 * A242605 A351396 A350598

Adjacent sequences: A132285 A132286 A132287 * A132289 A132290 A132291

Keyword

base,nonn

Author

Artur Jasinski, Aug 16 2007

Extensions

More terms from Michel Marcus, Nov 05 2013

Name edited by Robert Israel, Jan 05 2025

Status

approved