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A014613
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Numbers that are products of 4 primes (or 4-almost primes, a generalization of semiprimes).
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113
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16, 24, 36, 40, 54, 56, 60, 81, 84, 88, 90, 100, 104, 126, 132, 135, 136, 140, 150, 152, 156, 184, 189, 196, 198, 204, 210, 220, 225, 228, 232, 234, 248, 250, 260, 276, 294, 296, 297, 306, 308, 315, 328, 330, 340, 342, 344, 348, 350, 351, 364, 372, 375, 376
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Also called "quadruprimes". Divisible by exactly 4 prime powers (not including 1).
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..10000
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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FORMULA
| Product p_i^e_i with Sum e_i = 4.
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MATHEMATICA
| Select[Range[200], Plus @@ Last /@ FactorInteger[ # ] == 4 &] - Vladimir Orlovsky, Apr 23 2008
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PROG
| (PARI) isA014613(n) = bigomega(n)==4 [From Michael Porter (michael_b_porter(AT)yahoo.com), Dec 13 2009]
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CROSSREFS
| Cf. A033987, A114106 (number of 4-almost primes <= 10^n).
Sequences listing r-almost primes; that is the n such that A001222(n) = r: A000040 (r = 1), A001358 (r = 2), A014612 (r = 3), this sequence (r = 4), A014614 (r = 5), A046306 (r = 6), A046308 (r = 7), A046310 (r = 8), A046312 (r = 9), A046314 (r = 10), A069272 (r = 11), A069273 (r = 12), A069274 (r = 13), A069275 (r = 14), A069276 (r = 15), A069277 (r = 16), A069278 (r = 17), A069279 (r = 18), A069280 (r = 19), A069281 (r = 20). - Jason Kimberley, Oct 02 2011
Sequence in context: A036328 A067028 A110893 * A046370 A103248 A140135
Adjacent sequences: A014610 A014611 A014612 * A014614 A014615 A014616
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KEYWORD
| nonn
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AUTHOR
| Eric Weisstein (eric(AT)weisstein.com)
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EXTENSIONS
| More terms from Patrick De Geest (pdg(AT)worldofnumbers.com), Jun 15 1998.
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