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 A227011 Integers n such that phi(sigma(k))/sigma(phi(k)) >  phi(sigma(n))/sigma(phi(n)) for all k
 1, 3, 5, 11, 13, 17, 29, 41, 181, 209, 377, 779, 3239, 4469, 5249, 15539, 43259, 58589, 119279, 169679, 174719, 461369, 692687, 955499, 1258949, 1859129, 1917299, 3925463, 7991693, 8986469, 13244069, 16732169, 30629363, 44137523, 48466987, 64018433, 68787773 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS These are the indices where the rational function A062401(n)/A062402(n) drops below the minimum set by all earlier ratios. a(2) to a(9) are primes. However all known terms beginning from a(10) are composite. LINKS Donovan Johnson, Table of n, a(n) for n = 1..48 (terms < 10^10) EXAMPLE 5 is in the sequence because phi(sigma(5))/sigma(phi(5)) = 2/7 and for all k < 5, phi(sigma(k))/sigma(phi(k)) > 2/7. MAPLE A062401 := proc(n)     numtheory[phi](numtheory[sigma](n)) end proc: A062402 := proc(n)     numtheory[sigma](numtheory[phi](n)) end proc: s := proc(n)     A062401(n)/A062402(n) ; end proc: r := 100000000000000000000000000000 ; for n from 1 do     if s(n) < r then         printf("%d, \n", n) ;         r := s(n) ;     end if; end do: PROG (PARI) f(n)=eulerphi(sigma(n=factor(n)))/sigma(eulerphi(n)) is(n)=my(t=f(n)); for(k=1, n-1, if(f(k)<=t, return(0))); 1 \\ Charles R Greathouse IV, Nov 27 2013 CROSSREFS Cf. A227927, A062401, A062402, A033632, A229238. Sequence in context: A154500 A020578 A250481 * A243627 A178604 A153443 Adjacent sequences:  A227008 A227009 A227010 * A227012 A227013 A227014 KEYWORD nonn AUTHOR Vladimir Letsko, Oct 09 2013 EXTENSIONS a(33)-a(37) from Donovan Johnson, Oct 11 2013 STATUS approved

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Last modified April 23 13:25 EDT 2019. Contains 322386 sequences. (Running on oeis4.)