A067350 -id:A067350 - cp's OEIS frontend

A067349 Number of divisors of sigma(n)+phi(n).

2, 3, 4, 3, 4, 4, 4, 2, 2, 4, 4, 6, 4, 8, 6, 4, 4, 6, 4, 6, 6, 4, 4, 6, 4, 8, 4, 6, 4, 10, 4, 2, 6, 8, 12, 2, 4, 8, 10, 4, 4, 12, 4, 8, 8, 4, 4, 12, 6, 2, 8, 4, 4, 8, 10, 15, 6, 4, 4, 8, 4, 12, 12, 4, 12, 6, 4, 4, 12, 16, 4, 4, 4, 12, 6, 10, 12, 14, 4, 4, 6, 4, 4, 8, 6, 8, 10, 12, 4, 8, 8, 6, 6, 8

Offset: 1

Labos Elemer, Jan 17 2002

nonn

Amiram Eldar, Table of n, a(n) for n = 1..10000

Cf. A000005, A000010, A000203, A011774, A067350, A067351.

Table[ DivisorSigma[ 0, DivisorSigma[ 1, w ]+EulerPhi[ w ] ], {w, 1, 128} ]

a(n) = numdiv(sigma(n)+eulerphi(n)); \\ Michel Marcus, Aug 13 2019

a(n) = A000005(A000010(n) + A000203(n)).

A067351 Numbers k such that sigma(k) + phi(k) has exactly 2 distinct prime divisors.

Original entry on oeis.org

3, 5, 6, 7, 10, 11, 13, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 33, 35, 37, 39, 40, 41, 42, 43, 44, 46, 47, 49, 51, 52, 53, 55, 56, 57, 58, 59, 60, 61, 64, 66, 67, 68, 71, 72, 73, 75, 76, 78, 79, 80, 81, 82, 83, 84, 85, 87, 89, 91, 92, 93, 95, 96, 97

Offset: 1

Labos Elemer, Jan 17 2002

nonn

			Includes all odd primes and some composites; e.g., 21 and 25, since sigma(21) + phi(21) = 32 + 12 = 44 = 2*2*11; sigma(25) + phi(25) = 31 + 20 = 51 = 3*17.

G. C. Greubel, Table of n, a(n) for n = 1..1000

Cf. A000005, A000010, A000203, A001221, A065387, A067349, A067350.

Select[ Range[ 1, 100 ], Length[ FactorInteger[ DivisorSigma[ 1, # ]+EulerPhi[ # ] ] ]==2& ]
Select[Range[500], PrimeNu[EulerPhi[#] + DivisorSigma[1, #]] == 2 &] (* G. C. Greubel, May 08 2017 *)

a(n) = A001221(A000010(n) + A000203(n)) = A001221(A065387(n)) = 2.

Edited by Dean Hickerson, Jan 20 2002

cp's OEIS Frontend

A067349 Number of divisors of sigma(n)+phi(n).

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