A109028 - OEIS

%I #26 Mar 08 2024 18:34:26

%S 16560,25515,27864,42480,46872,51552,57348,61488,65448,67797,69408,

%T 69840,79776,80496,84375,84456,88416,105336,119448,125928,160416,

%U 167076,202032,204984,206928,210960,211104,211464,213750,213792,213920,213984

%N Numbers that have exactly eight prime factors counted with multiplicity (A046310) whose digit reversal is different and also has 8 prime factors (with multiplicity).

%C 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).

%H David A. Corneth, <a href="/A109028/b109028.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/AlmostPrime.html">Almost Prime</a>.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Emirp.html">Emirp</a>.

%H Eric Weisstein and Jonathan Vos Post, <a href="http://mathworld.wolfram.com/Emirpimes.html">Emirpimes</a>.

%e a(2) = 25515 is in this sequence because 25515 = 3^6 * 5 * 7 has exactly 8 prime factors counted with multiplicity and reverse(25515) = 51552 = 2^5 * 3^2 * 179 also has exactly 8 prime factors counted with multiplicity.

%o (PARI) is(n) = {

%o 	my(r = fromdigits(Vecrev(digits(n))));

%o 	n!=r && bigomega(n) == 8 && bigomega(r) == 8

%o } \\ _David A. Corneth_, Mar 07 2024

%Y Cf. A046310, A006567, A097393, A109018, A109023, A109024, A109025, A109026, A109027, A109029, A109030, A109031.

%K nonn,base

%O 1,1

%A _Jonathan Vos Post_, Jun 16 2005