OFFSET
1,1
COMMENTS
A073484(a(n)) = 1.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
78 is a term, as 78 = 2*3*13 with one gap between 3 and 13.
MAPLE
N:= 1000: # to get all terms <= N
Res:= NULL:
for a from 1 to numtheory:-pi(isqrt(N)) do
for b from a do
p:= mul(ithprime(i), i=a..b);
if p > N/ithprime(b+2) then break fi;
for c from b+2 while p*ithprime(c) <= N do
for d from c do
q:= mul(ithprime(i), i=c..d);
if p*q > N then break fi;
Res:= Res, p*q;
od
od
od
od:
sort([Res]); # Robert Israel, Apr 20 2017
MATHEMATICA
okQ[n_] := SquareFreeQ[n] && Length[SequencePosition[FactorInteger[n][[All, 1]], {p_?PrimeQ, q_?PrimeQ} /; q != NextPrime[p]]] == 1;
Select[Range[200], okQ] (* Jean-François Alcover, Feb 28 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Aug 03 2002
STATUS
approved