cp's OEIS Frontend

A109029 Numbers that have exactly nine prime factors counted with multiplicity (A046312) whose digit reversal is different and also has 9 prime factors (with multiplicity).

%I A109029 #27 Feb 16 2025 08:32:58
%S A109029 21168,23424,23616,27456,41184,42432,48114,61632,65472,86112,211410,
%T A109029 212256,213192,215232,217440,219072,230208,232512,236925,236928,
%U A109029 238656,238680,251100,251505,251748,253824,255024,255960,257856,259968,270912
%N A109029 Numbers that have exactly nine prime factors counted with multiplicity (A046312) whose digit reversal is different and also has 9 prime factors (with multiplicity).
%C A109029 This sequence is the k = 8 instance of the series which begins with k = 1 (emirps), k = 2, k = 3 (A109023), k = 4 (A109024), k = 5 (A109025), k = 6 (A109026), k = 7 (A109027), k = 8 (A109028).
%H A109029 David A. Corneth, <a href="/A109029/b109029.txt">Table of n, a(n) for n = 1..10000</a>
%H A109029 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AlmostPrime.html">Almost Prime</a>.
%H A109029 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Emirp.html">Emirp</a>.
%H A109029 Eric Weisstein and Jonathan Vos Post, <a href="https://mathworld.wolfram.com/Emirpimes.html">Emirpimes</a>.
%e A109029 a(1) = 21168 is in this sequence because 21168 = 2^4 * 3^3 * 7^2 has exactly 9 prime factors counted with multiplicity and reverse(21168) = 86112 = 2^5 * 3^2 * 13 * 23 also has exactly 9 prime factors counted with multiplicity.
%t A109029 okQ[n_]:=Module[{idn=IntegerDigits[n],ridn},ridn=Reverse[idn];idn!=ridn && PrimeOmega[n]==9&&PrimeOmega[FromDigits[ridn]]==9]; Select[Range[ 271000],okQ] (* _Harvey P. Dale_, Sep 24 2011 *)
%o A109029 (PARI) is(n) = {
%o A109029 	my(r = fromdigits(Vecrev(digits(n))));
%o A109029 	n!=r && bigomega(n) == 9 && bigomega(r) == 9
%o A109029 } \\ _David A. Corneth_, Mar 07 2024
%Y A109029 Cf. A046312, A006567, A097393, A109018, A109023, A109024, A109025, A109026, A109027, A109028, A109030, A109031.
%K A109029 nonn,base
%O A109029 1,1
%A A109029 _Jonathan Vos Post_, Jun 16 2005