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 A050438 Fourth-order composites. 3
 26, 33, 38, 39, 42, 49, 52, 55, 56, 60, 68, 69, 70, 74, 77, 78, 80, 84, 88, 93, 94, 95, 98, 100, 105, 106, 110, 115, 118, 119, 121, 124, 125, 126, 130, 133, 138, 140, 141, 145, 146, 152, 154, 155, 156, 159, 160, 162, 164, 165, 170, 174, 176, 180, 183, 184 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS N. Fernandez, An order of primeness, F(p) FORMULA Let C(n) be the n-th composite number, with C(1)=4. Then these are numbers C(C(C(C(n)))). EXAMPLE C(C(C(C(8)))) = C(C(C(15))) = C(C(25)) = C(38) = 55. So 55 is in the sequence. MAPLE C := remove(isprime, [\$4..1000]): seq(C[C[C[C[n]]]], n=1..100); CROSSREFS Sequence in context: A153224 A177210 A050770 * A047822 A048126 A080932 Adjacent sequences:  A050435 A050436 A050437 * A050439 A050440 A050441 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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