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A114434 To obtain a(n), write the n-th composite number as a product of primes, add 1 to each prime and multiply. 2

%I

%S 9,12,27,16,18,36,24,24,81,48,54,32,36,108,36,42,64,72,72,243,48,54,

%T 48,144,60,56,162,96,108,96,72,324,64,108,72,126,192,72,216,80,90,216,

%U 96,128,729,84,144,162,96,144,432,114,144,180,96,168,486,256

%N To obtain a(n), write the n-th composite number as a product of primes, add 1 to each prime and multiply.

%H Alois P. Heinz, <a href="/A114434/b114434.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A003959(A002808(n)). - _Michel Marcus_, Oct 22 2014

%p b:= proc(n) option remember; local k;

%p for k from 1+`if`(n=1, 3, b(n-1))

%p while isprime(k) do od; k

%p end:

%p a:= n-> mul((i[1]+1)^i[2], i=ifactors(b(n))[2]):

%p seq(a(n), n=1..100); # _Alois P. Heinz_, Oct 23 2014

%o (PARI) lista(nn) = {forcomposite(c=2, nn, f = factor(c); print1(prod(i=1, #f~, (f[i,1]+1)^f[i,2]), ", "););} \\ _Michel Marcus_, Jun 26 2013

%Y Cf. A002808, A003959, A249140.

%K nonn

%O 1,1

%A _Ben Paul Thurston_, May 06 2007

%E More terms from _Michel Marcus_, Jun 26 2013

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Last modified June 19 07:33 EDT 2019. Contains 324218 sequences. (Running on oeis4.)