A076578 - OEIS

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

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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.