login
A249353
a(n) = phi(n) + sigma(sigma(n)).
0
2, 5, 9, 10, 16, 30, 21, 28, 20, 43, 38, 60, 36, 66, 68, 40, 55, 62, 60, 104, 75, 101, 82, 176, 52, 108, 108, 132, 100, 203, 93, 120, 144, 136, 148, 124, 96, 186, 144, 250, 136, 264, 126, 244, 192, 217, 170, 240, 122, 148, 227, 195, 172, 378, 235, 384, 222, 262, 226, 496, 156, 282, 246, 160, 272, 423, 192, 344, 296, 427
OFFSET
1,1
COMMENTS
If n is a Mersenne prime then a(n) = 3n (see comments in A000668).
FORMULA
a(n) = A000010(n) + A000203(A000203(n)) = A000010(n) + A051027(n).
MATHEMATICA
Table[EulerPhi[n]+DivisorSigma[1, DivisorSigma[1, n]], {n, 70}] (* Harvey P. Dale, Feb 27 2020 *)
PROG
(Magma) [EulerPhi(n) + SumOfDivisors(SumOfDivisors(n)) : n in [1..100]]; // Vincenzo Librandi, Nov 15 2014
(PARI) vector(100, n, eulerphi(n)+sigma(sigma(n))) \\ Derek Orr, Nov 15 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Nov 14 2014
EXTENSIONS
Corrected and extended by Harvey P. Dale, Feb 27 2020
STATUS
approved