OFFSET
1,1
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000
FORMULA
a(n) == 1 (mod 4).
EXAMPLE
2413 is a term because 2413 = 19*127 is the product of two distinct primes, 2414 = 2*17*71 is the product of three distinct primes and 2415 = 3*5*7*23 is the product of four distinct primes.
6193 is a term because 6193 = 11*563 is the product of two distinct primes, 6194 = 2*19*163 is the product of three distinct primes and 6195 = 3*5*7*59 is the product of four distinct primes.
MAPLE
q:= n-> andmap(j-> map(i-> i[2], ifactors(n+j-2)[2])=[1$j], [$2..4]):
select(q, [$1..30000])[]; # Alois P. Heinz, Sep 21 2024
MATHEMATICA
Position[Partition[FactorInteger[#][[;; , 2]] & /@ Range[30000], 3, 1], {{1, 1}, {1, 1, 1}, {1, 1, 1, 1}}] // Flatten (* Amiram Eldar, Sep 21 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Massimo Kofler, Sep 21 2024
STATUS
approved