A369108 a(n) is the number of numbers less than or equal to 10^n that are divisible only by primes congruent to 1 mod 4.

2, 15, 123, 1074, 9623, 87882, 814183, 7618317, 71838469

Offset

1,1

Links

Table of n, a(n) for n=1..9.

Gareth A. Jones and Alexander K. Zvonkin, A number-theoretic problem concerning pseudo-real Riemann surfaces, arXiv:2401.00270 [math.NT], 2023. See Table 2 at page 7.

Mathematica

a[n_] := Length[Join[{1}, Select[Range[10^n], PrimeQ[f = First/@FactorInteger[#]] == Table[True, {j, PrimeNu[#]}] && Mod[f, 4] == Table[1, {m, PrimeNu[#]}] && #<=10^n &]]]; Array[a, 9]

Crossrefs

Cf. A004613, A369105, A369107, A369109, A369111.

Sequence in context: A185758 A052448 A168502 * A127610 A085228 A365157

Adjacent sequences: A369105 A369106 A369107 * A369109 A369110 A369111

Keyword

nonn,more

Author

Stefano Spezia, Jan 13 2024

Status

approved