A280729 (p-1)/2 + phi(p-1) as p runs through the odd primes.

2, 4, 5, 9, 10, 16, 15, 21, 26, 23, 30, 36, 33, 45, 50, 57, 46, 53, 59, 60, 63, 81, 84, 80, 90, 83, 105, 90, 104, 99, 113, 132, 113, 146, 115, 126, 135, 165, 170, 177, 138, 167, 160, 182, 159, 153, 183, 225, 186, 228, 215, 184, 225, 256, 261, 266, 207, 226, 236, 233

Offset: 1

Author

Vincenzo Librandi, Jan 10 2017

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A098006.

Programs

Magma

[(NthPrime(n)-1)/2+EulerPhi(NthPrime(n)-1): n in [2..100]];

Maple

A280729 := proc(n)
    local p;
    p := ithprime(n+1) ;
    (p-1)/2+numtheory[phi](p-1) ;
end proc: # R. J. Mathar, Jan 10 2017

Mathematica

Table[(n - 1)/2 + EulerPhi[n - 1], {n, Prime[Range[2, 100]]}]

Formula

a(n) = A098006(n)+2*A008330(n). - R. J. Mathar, Jan 10 2017