A136131 Values of n such that (sigma(sigma(n))-phi(phi(n)))/n is an integer (the corresponding integral ratios are given in A136132).

1, 3, 5, 18, 32, 36, 92, 144, 368, 576, 712, 800, 888, 918, 928, 1472, 3193, 4600, 4768, 8800, 9288, 10602, 13032, 16172, 21204, 26856, 36864, 56832, 61792, 84816, 93176, 94208, 96768, 160416, 229888, 339264, 441440, 589824, 670746, 746334, 834048, 893268

Offset

1,2

Links

Donovan Johnson, Table of n, a(n) for n = 1..92 (terms < 10^10)

Example

n = 92 is in the sequence because sigma(sigma(92))-phi(phi(92) = sigma(168)-phi(44) = 480-20 = 460 = 5*92.

Maple

with(numtheory): a:=proc(n) if type((sigma(sigma(n))-phi(phi(n)))/n, integer) =true then n else end if end proc: seq(a(n), n=1..100000);

Crossrefs

Cf. A136132, A138154, A137600.

Sequence in context: A358342 A039584 A191717 * A143546 A069066 A011964

Adjacent sequences: A136128 A136129 A136130 * A136132 A136133 A136134

Keyword

nonn

Author

Emeric Deutsch, Mar 03 2008

Status

approved