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A070802
a(n)=prevprime[sigma(n)]-nextprime[phi(n)]=A070801(n)-A070800(n).
1
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
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}]
KEYWORD
easy,nonn
AUTHOR
Labos Elemer, May 08 2002
STATUS
approved