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 A050436 Third-order composites. 7
 16, 21, 25, 26, 28, 33, 36, 38, 39, 42, 48, 49, 50, 52, 55, 56, 57, 60, 64, 68, 69, 70, 72, 74, 77, 78, 80, 84, 87, 88, 90, 93, 94, 95, 98, 100, 104, 105, 106, 110, 111, 115, 117, 118, 119, 121, 122, 124, 125, 126, 130, 133, 135, 138, 140, 141, 145, 146, 147 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS N. Fernandez, An order of primeness, F(p) N. Fernandez, An order of primeness [cached copy, included with permission of the author] FORMULA Let C(n) be the n-th composite number, with C(1)=4. Then these are numbers C(C(C(n))). EXAMPLE C(C(C(8))) = C(C(15)) = C(25) = 38. So 38 is in the sequence. MAPLE C := remove(isprime, [\$4..1000]): seq(C[C[C[C[n]]]], n=1..100); MATHEMATICA Nest[Values@ KeySelect[MapIndexed[First@ #2 -> #1 &, #], CompositeQ] &, Select[Range@ 150, CompositeQ], 2] (* Michael De Vlieger, Jul 22 2017 *) CROSSREFS Cf. A049076, A049077, A049078, A049079, A049080, A049081, A006450, A050435, A050438, ... Sequence in context: A290142 A165160 A180411 * A038868 A214515 A270783 Adjacent sequences: A050433 A050434 A050435 * A050437 A050438 A050439 KEYWORD easy,nonn AUTHOR Michael Lugo (mlugo(AT)thelabelguy.com), Dec 22 1999 EXTENSIONS More terms from Asher Auel (asher.auel(AT)reed.edu) Dec 15 2000 STATUS approved

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Last modified December 3 11:24 EST 2022. Contains 358517 sequences. (Running on oeis4.)