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Composite Flavius' numbers (A000960) whose divisors are again Flavius' numbers.
2

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

%S 39,49,91,133,763,15883,21207,32761,180739,268423,746607,2277163,

%T 28604419,93742347,13192600483,124387470307,3898087261291,

%U 13987912482103,69089500671469

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

%C Sequence A118130 is the analog for lucky numbers A000959.

%C a(20) > A000960(10^7). - _Donovan Johnson_, Aug 23 2012

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

%o (PARI) A181488(Nmax) = { my(S=[]); for(n=1, 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; fordiv(F,d,setsearch(S,d)||next(2)); print1(F", "))}

%K nonn

%O 1,1

%A _M. F. Hasler_, Oct 29 2010

%E a(13)-a(16) from _Donovan Johnson_, Oct 30 2010

%E a(17)-a(18) from _Donovan Johnson_, Nov 11 2010

%E a(19) from _Donovan Johnson_, Aug 23 2012