OFFSET
1,1
COMMENTS
A squarefree subsequence of 11-gonal numbers, i.e., numbers of the form k*(9*k-7)/2.
EXAMPLE
58 = 4*(9*4 - 7)/2 = 2*29;
141 = 6*(9*6 - 7)/2 = 3*47;
415 = 10*(9*10 - 7)/2 = 5*83;
3683 = 29*(9*29 - 7)/2 = 29*127.
MATHEMATICA
Select[Table[n*(9*n - 7)/2, {n, 1, 400}], FactorInteger[#][[;; , 2]] == {1, 1} &] (* Amiram Eldar, May 30 2022 *)
PROG
(Python)
from sympy import factorint
from itertools import count, islice
def agen():
for h in (k*(9*k - 7)//2 for k in count(1)):
f = factorint(h, multiple=True)
if len(f) == len(set(f)) == 2: yield h
print(list(islice(agen(), 37))) # Michael S. Branicky, May 30 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Massimo Kofler, May 30 2022
STATUS
approved