A121478 Triangular numbers with three distinct prime factors.

66, 78, 105, 120, 190, 231, 276, 300, 378, 406, 435, 465, 528, 561, 595, 666, 741, 820, 861, 903, 946, 1035, 1128, 1176, 1275, 1378, 1485, 1653, 1953, 2016, 2080, 2211, 2278, 2485, 2556, 2628, 2775, 3081, 3160, 3240, 3655, 3741, 3916, 4005, 4371, 4465

Offset

1,1

Links

Table of n, a(n) for n=1..46.

Example

11*12/2 = 2*3*11 = 66 is the smalles triangular number with three distinct prime factors, hence a(1) = 66.

Mathematica

Select[Accumulate[Range[0, 100]] , PrimeNu[#]==3&] (* James C. McMahon, Oct 19 2024 *)

Prog

(PARI) for(n=1, 100, k=binomial(n+1, 2); if(omega(k)==3, print1(k, ", ")))

Crossrefs

Cf. A000217, A068443, A119663, A121479.

Sequence in context: A036207 A039538 A095751 * A330809 A128896 A109750

Adjacent sequences: A121475 A121476 A121477 * A121479 A121480 A121481

Keyword

easy,nonn

Author

Klaus Brockhaus, Aug 01 2006

Status

approved