OFFSET
1,1
COMMENTS
Are there infinitely many such numbers?
These numbers have at least three prime factors.
If m and k are in the sequence, then lcm(m,k) is in the sequence. - Robert Israel, Jul 05 2017
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 1..398
EXAMPLE
4147 = 11*13*29 and lcm(12,14,30) = lcm(10,12,28) = 420.
13*23*29*41*43 multiplied by any divisor of 2*3*5*7*11.
MAPLE
filter:= proc(n) local F;
F:= ifactors(n)[2];
if max(seq(f[2], f=F)) > 1 then return false fi;
ilcm(seq(f[1]-1, f=F)) = ilcm(seq(f[1]+1, f=F))
end proc:
select(filter, [$2..10^6]); # Robert Israel, Jul 05 2017
MATHEMATICA
fQ[n_] := If[ SquareFreeQ@ n, Block[{p = First@ Transpose@ FactorInteger@ n}, LCM @@ (p - 1) == LCM @@ (p + 1)], False]; Select[ Range[10^6], fQ] (* Robert G. Wilson v, Jun 05 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, May 26 2017
EXTENSIONS
More terms from Robert G. Wilson v, Jun 05 2017
STATUS
approved