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a(n) = sigma(n) mod PrimePi(n).
3

%I #19 Sep 08 2022 08:45:06

%S 0,0,1,0,0,0,3,1,2,2,3,2,0,0,1,4,4,4,2,0,4,6,6,4,6,4,2,0,2,10,8,4,10,

%T 4,3,2,0,8,6,3,5,2,0,8,2,3,4,12,3,12,8,6,8,8,8,0,10,9,15,8,6,14,1,12,

%U 0,11,12,1,11,12,15,11,9,19,14,12,0,14,10,11,16,15,17,16,17,5,19,18,18

%N a(n) = sigma(n) mod PrimePi(n).

%H Michael De Vlieger, <a href="/A072548/b072548.txt">Table of n, a(n) for n = 2..10000</a>

%F a(n) = A000203(n) mod A000720(n).

%p with(numtheory): seq(modp(sigma(n),pi(n)),n=2..100); # _Muniru A Asiru_, Dec 10 2018

%t Table[Mod[DivisorSigma[1, w], PrimePi[w]], {w, 1, 128}]

%o (PARI) a(n) = sigma(n) % primepi(n); \\ _Michel Marcus_, Dec 10 2018

%o (Magma) [SumOfDivisors(n) mod (#PrimesUpTo(n)): n in [2..100]]; // _Vincenzo Librandi_, Dec 10 2018

%Y Cf. A000203, A000720, A073321, A073322, A073323, A073324.

%K nonn

%O 2,7

%A _Labos Elemer_, Aug 05 2002