A354446 11-gonal numbers which are products of three distinct primes.

30, 506, 606, 715, 1558, 1730, 3945, 5083, 6365, 8558, 9361, 11986, 12455, 14935, 15458, 17081, 19371, 19966, 21183, 25726, 29971, 32215, 32981, 37766, 45551, 46461, 51146, 54065, 57065, 58083, 62245, 68758, 74433, 75595, 76766, 80333, 86458, 88971, 90241

Offset: 1

Author

Massimo Kofler, Jun 01 2022

Keywords

• nonn

Comments

A squarefree subsequence of 11-gonal numbers.

Examples

			     30 =   3*(9*3   - 7)/2 =  2 *  3 *   5;
    506 =  11*(9*11  - 7)/2 =  2 * 11 *  23;
   3945 =  30*(9*30  - 7)/2 =  3 *  5 * 263;
  80333 = 134*(9*134 - 7)/2 = 11 * 67 * 109.
		

Crossrefs

Intersection of A051682 and A007304.

Programs

Maple

q:= n-> is(map(x-> x[2], ifactors(n)[2])=[1$3]):
select(q, [n*(9*n-7)/2$n=1..200])[];  # Alois P. Heinz, Jun 15 2022

Mathematica

Select[Table[n*(9*n-7)/2, {n, 1, 150}], FactorInteger[#][[;; , 2]]=={1, 1, 1} &] (* Amiram Eldar, Jun 01 2022 *)