A227927 Numbers n such that phi(sigma(k))/sigma(phi(k)) < phi(sigma(n))/sigma(phi(n)) for all k < n and n is the smallest positive integer with this property.

1, 2, 36, 144, 576, 3600, 14400, 921600, 1040400, 4161600, 8643600, 34574400, 266342400, 700131600, 2800526400, 179233689600, 202338032400, 809352129600

Offset

1,2

Comments

All known terms excluding a(2) are perfect squares.

Links

Table of n, a(n) for n=1..18.

Example

36 is in the sequence because phi(sigma(36))/sigma(phi(36)) = 18/7 and for all k < 36 phi(sigma(k))/sigma(phi(k)) < 18/7.

Maple

s:= n -> numtheory:-phi(numtheory:-sigma(n))/numtheory:-sigma(numtheory:-phi(n)):
  a, na, A[1], sA[1]:=1, 1, 1, 1:
1; for i from 2 do ss:=s(i): if ss>a then na:=na+1:A[na]:=ss:a:=ss:sA[na]:=i:print(sA[na]) fi od:

Crossrefs

Cf. A227011, A062401, A062402, A033632, A229238.

Sequence in context: A143745 A199944 A357445 * A007757 A141217 A206688

Adjacent sequences: A227924 A227925 A227926 * A227928 A227929 A227930

Keyword

nonn

Author

Vladimir Letsko, Oct 09 2013

Status

approved