A076578 Triangular numbers which are 4-almost primes.

36, 136, 210, 276, 351, 666, 820, 1035, 1225, 1275, 1326, 1431, 1770, 1830, 1953, 2145, 2346, 2415, 2775, 2926, 3003, 3486, 3916, 4005, 4186, 4278, 5050, 5356, 5565, 6105, 6555, 6670, 6903, 7626, 8001, 8385, 8646, 9316, 9730, 10731, 11175, 11325, 11476, 11935

Offset: 1

Author

Shyam Sunder Gupta, Oct 19 2002

Keywords

• easy
• nonn

Examples

			36 is a term because it is a triangular number and 36 = 2*2*3*3, i.e., is a product of 4 prime factors so is a 4-almost prime.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Intersection of A000217 and A014613.

Cf. A068443, A075875.

Programs

Maple

q:= n-> is(numtheory[bigomega](n)=4):
select(q, [i*(i+1)/2$i=0..200])[];  # Alois P. Heinz, Mar 27 2024

Mathematica

q[n_] := PrimeOmega[n] == 4;
Select[Table[i*(i+1)/2, {i, 0, 200}], q] (* Jean-François Alcover, Jan 13 2025, after Alois P. Heinz *)