A050436 Third-order composites.

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

Offset

1,1

Links

Table of n, a(n) for n=1..59.

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 Dec 15 2000

Status

approved