1,2

sigma_1(n) is the sum of the divisors of n [same as sigma(n)] (A000203).

Jud McCranie, Table of n, a(n) for n = 1..10000 (first 800 terms from Vincenzo Librandi)

Select[ Array[ DivisorSigma[ 1, # ]/EulerPhi[ # ]&, 20000 ], IntegerQ ]

(MAGMA) [ q: n in [1..20000] | r eq 0 where q, r is Quotrem(SumOfDivisors(n), EulerPhi(n)) ]; // Klaus Brockhaus, Nov 09 2008

Cf. A000010, A000203, A020492.

Sequence in context: A196518 A207636 A125764 * A267100 A178754 A276446

Adjacent sequences: A023894 A023895 A023896 * A023898 A023899 A023900

nonn

Olivier Gérard

approved