A226586 Odd values of sigma(n) - phi(n) in the order of appearance and with repetition.

5, 11, 7, 23, 33, 11, 47, 79, 15, 73, 95, 171, 67, 129, 177, 23, 191, 355, 309, 27, 315, 385, 283, 289, 383, 723, 35, 739, 393, 39, 687, 801, 489, 1089, 711, 767, 47, 1459, 649, 281, 1599, 969, 801, 607, 1431, 1633, 59, 1971, 2581, 63, 1555, 1535, 1153, 1069, 2931, 1605, 927, 1843, 3319, 2121

Offset: 1

Author

Wesley Ivan Hurt, Jun 28 2013

Keywords

• nonn

Comments

Odd values of A051612(n) sorted along n.

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A051612, A028982.

Programs

Maple

select(type, [seq(numtheory:-sigma(n)-numtheory:-phi(n), n=1..2000)], odd); # Robert Israel, Aug 11 2019

Mathematica

Select[Table[DivisorSigma[1,n]-EulerPhi[n],{n,2000}],OddQ] (* Harvey P. Dale, Sep 27 2013 *)

Formula

sigma(4) - phi(4) = 7 - 2 = 5. Since 5 is the first odd value of sigma(n) - phi(n), it appears first in the list. So a(1) = 5.