OFFSET
1,3
COMMENTS
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
Since 10 = 2*5, 2 = prime(1), and 5 = prime(3), a(10) = 1*1 = 1.
Since 9 = 3^2 and 3 is an even-indexed prime, 3 = prime(2), then a(9) = 3^2 = 9.
Since 35 = 5*7, 5 = prime(3), and 7 = prime(4), we see that a(35) = 1*7 = 7.
MATHEMATICA
f[n_] := Block[{a, g, pf = FactorInteger@ n}, a = PrimePi[First /@ pf]; g[x_] := If[Or[OddQ@ x, x == 0], 1, Prime@ x]; Times @@ Power @@@ Transpose@ {g /@ a, Last /@ pf}]; Array[f, 120] (* Michael De Vlieger, Mar 03 2015 *)
Array[Times @@ (FactorInteger[#] /. {p_, e_} /; e > 0 :> (p^Mod[PrimePi@ p + 1, 2])^e) &, 79] (* Michael De Vlieger, Apr 05 2017 *)
PROG
(Sage)
n=100; evenIndexPrimes=[primes_first_n(2*n+2)[2*i+1] for i in [0..n]]
[prod([(x[0]^(x[0] in evenIndexPrimes))^x[1] for x in factor(n)]) for n in [1..n]]
(PARI) a(n) = {f = factor(n); for (i=1, #f~, f[i, 2] *= (primepi(f[i, 1])+1) % 2; ); factorback(f); } \\ Michel Marcus, Mar 03 2015
(Haskell)
a248101 = product . filter (even . a049084) . a027746_row
-- Reinhard Zumkeller, Mar 06 2015
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Tom Edgar, Mar 03 2015
STATUS
approved