OFFSET
1,2
FORMULA
a(p) = 2p + 1 for p = odd primes (A065091).
EXAMPLE
a(6) = lcm(1, tau(1)) + lcm(2, tau(2)) + lcm(3, tau(3)) + lcm(6, tau(6)) = lcm(1, 1) + lcm(2, 2) + lcm(3, 2) + lcm(6, 4) = 1 + 2 + 6 + 12 = 21.
MATHEMATICA
a[n_] := DivisorSum[n, LCM[#, DivisorSigma[0, #]] &]; Array[a, 100] (* Amiram Eldar, May 10 2020 *)
PROG
(Magma) [&+[LCM(d, #Divisors(d)): d in Divisors(n)]: n in [1..100]]
(PARI) a(n) = sumdiv(n, d, lcm(d, numdiv(d))); \\ Michel Marcus, May 10 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, May 10 2020
STATUS
approved