A163178 - OEIS

A163178

a(n) is the central prime factor of A046339(n).

2, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 5, 2, 3, 3, 2, 5, 2, 5, 2, 3, 2, 2, 7, 3, 3, 5, 3, 5, 2, 3, 2, 3, 2, 2, 5, 2, 5, 3, 7, 2, 3, 7, 3, 2, 5, 2, 5, 3, 2, 3, 5, 2, 3, 7, 3, 2, 5, 2, 5, 2, 3, 2, 2, 3, 5, 7, 2, 7, 11, 3, 2, 7, 3, 3, 5, 3, 3, 2, 7, 2, 3, 2, 7, 5, 3, 2, 3, 2, 5, 11, 2, 5, 2, 3, 2, 5, 2, 2, 3, 2, 7, 5

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..104.

EXAMPLE

a(8)=2 since A046339(8) = 32 = 2*2*2*2*2.

a(9)=3 since A046339(9) = 42 = 2*3*7.

a(10)=2 since A046339(10) = 44 = 2*2*11.

a(11)=3 since A046339(11) = 45 = 3*3*5.

a(12)=2 since A046339(12) = 48 = 2*2*2*2*3.

MAPLE

cpr := proc(n) nred := n ; while numtheory[bigomega](nred) > 1 do pf := sort(convert(numtheory[factorset](nred), list)) ; nred := nred/op(1, pf)/op(-1, pf) ; od: nred ; end:

A046339 := proc(n) option remember ; if n = 1 then 8 ; else for a from procname(n-1)+1 do if not isprime(a) and numtheory[bigomega](a) mod 2 = 1 then RETURN(a) ; fi; od: fi; end:

A163178 := proc(n) cpr(A046339(n)) ; end; seq(A163178(n), n=1..120) ; # R. J. Mathar, Jul 25 2009

CROSSREFS

Cf. A046339, A162361.

Sequence in context: A024677 A276856 A174296 * A219545 A029374 A255933

Adjacent sequences: A163175 A163176 A163177 * A163179 A163180 A163181

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jul 22 2009

EXTENSIONS

More terms from R. J. Mathar, Jul 25 2009

STATUS

approved