A070802 a(n)=prevprime[sigma(n)]-nextprime[phi(n)]=A070801(n)-A070800(n).

1, 0, 4, 0, 8, 0, 8, 6, 12, 0, 18, 0, 16, 12, 20, 0, 30, 0, 30, 18, 20, 0, 48, 8, 28, 18, 40, 0, 60, 0, 44, 24, 36, 18, 76, 0, 40, 24, 72, 0, 76, 0, 60, 44, 48, 0, 96, 10, 66, 34, 68, 0, 94, 30, 84, 42, 60, 0, 150, 0, 58, 66, 90, 30, 116, 0, 76, 42, 110, 0, 164, 0, 76, 72, 102, 28

Offset

2,3

Links

Table of n, a(n) for n=2..77.

Formula

a(n)=p[Pi(sigma[n])]-p[1+Pi(phi[n])]

Example

n=100:sigma[100]=217,prevprime[217]=211, phi[100]=40,nextprime[40]=41,a(100)=211-41=170. The difference is 0 for odd primes.

Mathematica

Table[Prime[PrimePi[DivisorSigma[1, w]]]- Prime[1+PrimePi[EulerPhi[w]]], {w, 2, 128}]

Crossrefs

Cf. A007917, A007818, A000010, A000203, A000720, A000040, A070800, A070801.

Sequence in context: A222609 A247848 A076261 * A114401 A378617 A304440

Adjacent sequences: A070799 A070800 A070801 * A070803 A070804 A070805

Keyword

easy,nonn

Author

Labos Elemer, May 08 2002

Status

approved