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

1,1

Links

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

Example

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.

Maple

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

Crossrefs

Cf. A000217, A014613, A068443, A075875.

Sequence in context: A196891 A105090 A254284 * A044368 A044749 A067865

Adjacent sequences: A076575 A076576 A076577 * A076579 A076580 A076581

Keyword

easy,nonn

Author

Shyam Sunder Gupta, Oct 19 2002

Status

approved