A141676 - OEIS

%I #23 Sep 08 2022 08:45:35

%S 1,7,8,10,14,15,19,20,21,22,24,30,37,38,39,40,42,46,53,54,55,56,57,58,

%T 62,65,66,70,71,72,78,82,88,89,90,91,92,93,94,95,96,102,104,105,107,

%U 108,110,114,115,118,119,120,122,123,125,126,128,130,131,132,133,134,135

%N Numbers k such that (sigma_0(k) * PrimePi(k)) == 0 (mod 8).

%H G. C. Greubel, <a href="/A141676/b141676.txt">Table of n, a(n) for n = 1..5000</a>

%t Flatten[Table[If[Mod[DivisorSigma[0, n]*PrimePi[n], 8] == 0, n, {}], {n, 1, 200}]]

%t Select[Range[200],Divisible[DivisorSigma[0,#]PrimePi[#],8]&] (* _Harvey P. Dale_, Apr 29 2022 *)

%o (PARI) for(n=1, 150, if(Mod(sigma(n,0)*primepi(n),8)==0, print1(n", "))) \\ _G. C. Greubel_, Apr 02 2019

%o (Magma) [n: n in [1..150] | NumberOfDivisors(n)*#PrimesUpTo(n) mod 8 eq 0 ]; // _G. C. Greubel_, Apr 02 2019

%o (Sage) [n for n in (1..150) if mod(sigma(n, 0)*prime_pi(n), 8)==0 ] # _G. C. Greubel_, Apr 02 2019

%Y Cf. A000005 (sigma_0), A000720 (PrimePi).

%K nonn

%O 1,2

%A _Roger L. Bagula_, Sep 07 2008

%E Edited by _G. C. Greubel_, Apr 02 2019