OFFSET
1,3
COMMENTS
Write down phi(1), phi(2), phi(3), ..., then sort this list. Of course the list before sorting is simply sequence A000010.
To ensure that all terms are found, the values of phi(n) should be computed for all n up to a primorial p# -- which are the local minima of the phi function. Selecting and sorting the values of phi(n) <= phi(p#) produces the terms of this sequence. - T. D. Noe, Mar 22 2011
LINKS
Zak Seidov, Table of n, a(n) for n=1..9999 (values up to 5152)
MATHEMATICA
Cases[Sort[Table[EulerPhi[n], {n, 1, 36^2}]], n_ /; n<=36 ] (* Jean-François Alcover, Mar 22 2011 *)
A007614[m_]:=Select[Sort[Table[EulerPhi[n], {n, Prime[m]}]], #≤m&]; A007614[1000] (* Zak Seidov, Mar 22 2011 *)
primorial = Times @@ Prime[Range[4]]; phi = EulerPhi[primorial]; Sort[Select[EulerPhi[Range[primorial]], # <= phi &]] (* T. D. Noe, Mar 22 2011 *)
PROG
(PARI) (See A032447).
(Haskell)
import Data.List.Ordered (insertBag)
a007614 n = a007614_list !! (n-1)
a007614_list = f [1..] a002110_list [] where
f xs'@(x:xs) ps'@(p:ps) us
| x < p = f xs ps' $ insertBag (a000010' x) us
| otherwise = vs ++ f xs' ps ws
where (vs, ws) = span (<= a000010' x) us
-- Reinhard Zumkeller, Nov 22 2015
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
STATUS
approved