A072917 a(n) = p(n) - phi(n), where p(n) is the least prime greater than phi(n).

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 1, 1, 1, 3, 1, 1, 1, 3, 3, 1, 1, 1, 1, 3, 1, 1, 3, 1, 5, 1, 1, 1, 5, 1, 1, 1, 1, 3, 5, 1, 1, 1, 1, 3, 5, 5, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 5, 5, 3, 1, 5, 3, 5, 1, 5, 1, 1, 1, 1, 1, 5, 1, 5, 5, 1, 1, 5, 3, 1, 3, 1, 1, 5, 1, 3, 1, 1, 1, 5, 1, 1, 1, 1

Offset

1,15

Links

Antti Karttunen, Table of n, a(n) for n = 1..10000

Formula

a(n) = A013632(A000010(n)). - Antti Karttunen, Aug 22 2017

Example

phi(15) = 8 and the least prime > 8 is 11; hence a(15) = 11 - 8 = 3.

Mathematica

a[n_] := Module[{r, p}, p = EulerPhi[n]; r = p + 1; While[ ! PrimeQ[r], r = r + 1]; r - p]; Table[a[i], {i, 1, 100}]
lpg[n_]:=Module[{ep=EulerPhi[n]}, NextPrime[ep]-ep]; Array[lpg, 200] (* Harvey P. Dale, May 29 2017 *)

Prog

(PARI) A072917(n) = (nextprime(1+eulerphi(n)) - eulerphi(n)); \\ Antti Karttunen, Aug 22 2017

Crossrefs

Cf. A000010, A013632, A072344.

Sequence in context: A079075 A086703 A242849 * A319861 A114266 A230206

Adjacent sequences: A072914 A072915 A072916 * A072918 A072919 A072920

Keyword

easy,nonn

Author

Joseph L. Pe, Aug 11 2002

Status

approved