OFFSET
1,1
COMMENTS
Indices such that the sum of the nontrivial divisors and of the Euler totient function at that index is prime.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..5000
EXAMPLE
n=3 is in the sequence because Chowla(3) + phi(3) = 0 + 2 = 2 (a prime);
n=6 is in the sequence because Chowla(6) + phi(5) = 5 + 2 = 7 (a prime).
MAPLE
A048050 := proc(n) if n = 1 then 0; else numtheory[sigma](n)-n-1 ; fi; end:
A000010 := proc(n) numtheory[phi](n) ; end: isA164114 := proc(n) isprime( A000010(n)+A048050(n)) ; end:
for n from 1 to 400 do if isA164114(n) then printf("%d, ", n): fi; od: # R. J. Mathar, Aug 27 2009
MATHEMATICA
f[n_] := Plus @@ Divisors[n] - n - 1; Select[Range[100], PrimeQ[f[#] + EulerPhi[#]] &] (* G. C. Greubel, Sep 11 2017 *)
PROG
(PARI) isok(n) = isprime(sigma(n)+eulerphi(n)-n-1); \\ Michel Marcus, Sep 12 2017
(Magma) [n: n in [1..400] | IsPrime((SumOfDivisors(n)+EulerPhi(n))-n-1)]; // Vincenzo Librandi, Sep 12 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Aug 10 2009
EXTENSIONS
34 and 60 removed, 54 inserted by R. J. Mathar, Aug 27 2009
STATUS
approved