login
Composite Flavius' numbers (A000960) whose prime factors are again Flavius' numbers.
1

%I #13 Aug 05 2024 18:17:25

%S 27,39,49,63,91,133,147,399,567,763,2187,13239,15379,15883,21207,

%T 32761,151599,173563,180739,268423,746607,2277163,2557359,3114783,

%U 8218083,28604419,65002743,68944959,91727883,93742347,237963999,310488507

%N Composite Flavius' numbers (A000960) whose prime factors are again Flavius' numbers.

%C Contains A181488 as a subsequence.

%H Klaus Brockhaus, <a href="/A181489/b181489.txt">Table of n, a(n) for n = 1..50</a>

%H <a href="/index/J#Josephus">Index entries for sequences related to the Josephus Problem</a>

%o (PARI) A181489(Nmax) = { my(S=[]); for(n=2, Nmax, my(F=n);for(i=1,n-1,F=(n-i)*ceil(F/(n-i)+1)); S=setunion(S,Set(F)); isprime(F) & next; for(i=1,#F=factor(F)~,setsearch(S,F[1,i])||next(2)); print1(factorback(F~),", "))}

%K nonn

%O 1,1

%A _M. F. Hasler_, Oct 29 2010

%E a(22)-a(32) from _Donovan Johnson_ and _Klaus Brockhaus_, Oct 30 2010