A152991 a(n) = sigma(n) - pi(n).

1, 2, 2, 5, 3, 9, 4, 11, 9, 14, 7, 23, 8, 18, 18, 25, 11, 32, 12, 34, 24, 28, 15, 51, 22, 33, 31, 47, 20, 62, 21, 52, 37, 43, 37, 80, 26, 48, 44, 78, 29, 83, 30, 70, 64, 58, 33, 109, 42, 78, 57, 83, 38, 104, 56, 104, 64, 74, 43, 151, 44, 78, 86, 109, 66, 126, 49, 107, 77, 125, 52

Offset: 1

Author

Omar E. Pol, Dec 19 2008

Keywords

• easy
• nonn

Comments

a(n) = A000203(n) - A000720(n). - Omar E. Pol, Dec 21 2008

Examples

			a(15) = 24 - 6 = 18 because the sum of the divisors of 15 is 1 + 3 + 5 + 15 = 24 and there are 6 primes not exceeding 15 (2, 3, 5, 7, 11 and 13). - _Emeric Deutsch_, Dec 29 2008
		

Links

• Michel Marcus, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A000203, A000720, A152770.

Programs

Maple

with(numtheory): seq(sigma(n)-pi(n), n = 1 .. 80); # Emeric Deutsch, Dec 29 2008

Mathematica

Table[DivisorSigma[1,n]-PrimePi[n],{n,80}] (* Harvey P. Dale, Oct 20 2021 *)

PARI

a(n) = sigma(n) - primepi(n); \\ Michel Marcus, Jun 18 2019

Extensions

Corrected and extended by Emeric Deutsch, Dec 29 2008