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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
9, 12, 27, 16, 18, 36, 24, 24, 81, 48, 54, 32, 36, 108, 36, 42, 64, 72, 72, 243, 48, 54, 48, 144, 60, 56, 162, 96, 108, 96, 72, 324, 64, 108, 72, 126, 192, 72, 216, 80, 90, 216, 96, 128, 729, 84, 144, 162, 96, 144, 432, 114, 144, 180, 96, 168, 486, 256 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = A003959(A002808(n)). - Michel Marcus, Oct 22 2014
MAPLE
b:= proc(n) option remember; local k;
for k from 1+`if`(n=1, 3, b(n-1))
while isprime(k) do od; k
end:
a:= n-> mul((i[1]+1)^i[2], i=ifactors(b(n))[2]):
seq(a(n), n=1..100); # Alois P. Heinz, Oct 23 2014
MATHEMATICA
f[n_] := Module[{p, e},
Product[{p, e} = pe; (p+1)^e, {pe, FactorInteger[n]}]];
f /@ Select[Range[1000], CompositeQ] (* Jean-François Alcover, Jul 11 2021 *)
PROG
(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
CROSSREFS
Sequence in context: A328069 A014766 A182877 * A105704 A216192 A340040
KEYWORD
nonn
AUTHOR
Ben Paul Thurston, May 06 2007
EXTENSIONS
More terms from Michel Marcus, Jun 26 2013
STATUS
approved

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Last modified March 28 14:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)