OFFSET
1,1
LINKS
Reinhard Zumkeller and Donovan Johnson, Table of n, a(n) for n = 1..500 (first 150 terms from Reinhard Zumkeller)
FORMULA
A001414(a(n)) mod A001222(a(n)) = 0 and A001414(a(n))/A001222(a(n)) = 3. [Reinhard Zumkeller, Nov 20 2011]
EXAMPLE
20 is in the sequence because 20 = 2*2*5 and (2+2+5)/3 = 9/3 = 3.
MAPLE
for i from 2 to 35000 do: a:=ifactors(i): s:=sum((a[2][j][1]*a[2][j][2]), j=1..nops(a[2])): t:=sum((a[2][j][2]), j=1..nops(a[2])): if s/t=3 then print(i); fi od:
MATHEMATICA
Select[Range[61000], Mean[Flatten[Table[#[[1]], {#[[2]]}]&/@FactorInteger[ #]]]==3&] (* Harvey P. Dale, Nov 08 2013 *)
PROG
(Haskell)
a200612 n = a200612_list !! (n-1)
a200612_list = filter f [2..] where
f x = r == 0 && x' == 3 where (x', r) = divMod (a001414 x) (a001222 x)
-- Reinhard Zumkeller, Nov 20 2011
(PARI) isok(n) = my(f = factor(n)); (sum(k=1, #f~, f[k, 1]*f[k, 2]) / vecsum(f[, 2])) == 3; \\ Michel Marcus, Feb 22 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Jeffrey Burch, Nov 19 2011
STATUS
approved