A050439 - OEIS

%I #7 Oct 27 2023 22:00:44

%S 39,49,55,56,60,69,74,77,78,84,93,94,95,100,105,106,110,115,119,124,

%T 125,126,130,133,140,141,145,152,155,156,159,162,164,165,170,174,180,

%U 183,184,188,189,198,201,202,203,206,207,209,212,213,218,222,225,231

%N Fifth-order composites.

%H N. Fernandez, <a href="http://www.borve.org/primeness/FOP.html">An order of primeness, F(p)</a>

%H N. Fernandez, <a href="/A006450/a006450.html">An order of primeness</a> [cached copy, included with permission of the author]

%F Let C(n) be the n-th composite number, with C(1)=4. Then these are numbers C(C(C(C(C(n))))).

%e C(C(C(C(C(8))))) = C(C(C(C(15)))) = C(C(C(25))) = C(C(38)) = C(55) = 77. So 77 is in the sequence.

%p C := remove(isprime,[$4..1000]): seq(C[C[C[C[C[n]]]]],n=1..100);

%Y Cf. A049076-A049081, A006450, A050435, A050436, A050438, A050440.

%K easy,nonn

%O 1,1

%A Michael Lugo (mlugo(AT)thelabelguy.com), Dec 22 1999

%E More terms from _Asher Auel_ Dec 15 2000