A240528 Indices of 8-almost prime triangular numbers.

63, 80, 128, 256, 287, 288, 319, 320, 324, 383, 399, 440, 447, 480, 495, 539, 560, 567, 576, 608, 640, 648, 671, 675, 703, 720, 729, 799, 831, 863, 927, 935, 972, 975, 1000, 1007, 1055, 1056, 1071, 1079, 1080, 1104, 1119, 1120, 1160, 1175, 1183, 1184

Offset

1,1

Links

Muniru A Asiru, Table of n, a(n) for n = 1..10000 (first 1000 terms from Vincenzo Librandi)

Formula

{ m : A069904(m) = 8 }. - Alois P. Heinz, Aug 05 2019

Example

a(1) = 63 because A000217(63) = 63*(63+1)/2 = 2016 = 2^5 * 3^2 * 7 is an 8-almost prime.

Mathematica

Flatten[Position[Accumulate[Range[1500]], _?(PrimeOmega[#]== 8 &)]]

Prog

(GAP) F:=List([1..1200], n->Length(Factors(n*(n+1)/2)));; a:=Filtered([1..Length(F)], i->F[i]=8); # Muniru A Asiru, Dec 22 2018
(Magma) [n: n in [2..1200] | &+[d[2]: d in Factorization((n*(n+1)))] eq 9]; // Vincenzo Librandi, Dec 22 2018

Crossrefs

Cf. A000217, A069904, A108815, A114435, A114436, A114437, A164977.

Cf. A046310 (8-almost primes).

Sequence in context: A238088 A350960 A046049 * A320066 A125112 A043186

Adjacent sequences: A240525 A240526 A240527 * A240529 A240530 A240531

Keyword

nonn

Author

Vincenzo Librandi, Apr 07 2014

Status

approved