A141676 - OEIS

A141676

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

1, 7, 8, 10, 14, 15, 19, 20, 21, 22, 24, 30, 37, 38, 39, 40, 42, 46, 53, 54, 55, 56, 57, 58, 62, 65, 66, 70, 71, 72, 78, 82, 88, 89, 90, 91, 92, 93, 94, 95, 96, 102, 104, 105, 107, 108, 110, 114, 115, 118, 119, 120, 122, 123, 125, 126, 128, 130, 131, 132, 133, 134, 135

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..5000

MATHEMATICA

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

Select[Range[200], Divisible[DivisorSigma[0, #]PrimePi[#], 8]&] (* Harvey P. Dale, Apr 29 2022 *)

PROG

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

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

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

CROSSREFS

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

Sequence in context: A080113 A243078 A048588 * A127164 A153972 A286420

Adjacent sequences: A141673 A141674 A141675 * A141677 A141678 A141679

KEYWORD

nonn

AUTHOR

Roger L. Bagula, Sep 07 2008

EXTENSIONS

Edited by G. C. Greubel, Apr 02 2019

STATUS

approved