OFFSET
1,1
COMMENTS
A squarefree subsequence of 11-gonal numbers, i.e., numbers of the form k*(9*k-7)/2.
EXAMPLE
4785 = 33*(9*33-7)/2 = 3*5*11*29.
30710 = 83*(9*83-7)/2 = 2*5*37*83.
140361 = 177*(9*177-7)/2 = 3*13*59*61.
303290 = 260*(9*260-7)/2 = 2*5*13*2333.
MAPLE
q:= n-> is(map(x-> x[2], ifactors(n)[2])=[1$4]):
select(q, [n*(9*n-7)/2$n=1..300])[]; # Alois P. Heinz, Jun 15 2022
MATHEMATICA
Select[Table[n*(9*n - 7)/2, {n, 1, 300}], FactorInteger[#][[;; , 2]] == {1, 1, 1, 1} &] (* Amiram Eldar, Jun 08 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Massimo Kofler, Jun 08 2022
STATUS
approved