A289777 Frequency of the largest spectral component of the prime characteristic function of the first n numbers, for n>3, excluding the smallest and largest frequencies. In case of a tie, use the smallest frequency.

2, 2, 3, 3, 4, 3, 5, 5, 4, 6, 6, 4, 7, 7, 7, 8, 8, 5, 9, 9, 9, 6, 6, 6, 6, 11, 11, 7, 12, 12, 7, 13, 13, 14, 14, 14, 15, 15, 15, 8, 16, 16, 17, 17, 17, 11, 18, 18, 10, 10, 19, 12, 20, 20, 11, 11, 21, 21, 22, 22, 12, 23, 23, 12, 24, 24, 13, 25, 25, 13, 26, 26, 14, 27, 27, 14, 28, 28, 29, 29, 29, 15, 30, 30, 16, 16

Offset

4,1

Comments

The Discrete Fourier transform is applied to the list of the prime characteristic function (A010051) of the first n numbers; then the position of the largest absolute value of the components of the transformed list, disregarding the first and last components, is selected. If there are several identical maxima then the lowest position of them is taken.

The scatter plot of these maximum spectral components exhibits a curious pattern in which these components are essentially aligned along two convergent directions (see link).

It seems that the Fourier spectrum of the prime characteristic function is remarkably symmetric when obtained from a list with an even numer of elements (see link) and it could be related to the symmetry found in the distribution of consecutive and alternate primes gap ratios (see comments and plots in A274263 and A276309).

Conjecture: lim_{n->inf} abs(4a(n)/n - 1) = 1/3.

Links

Table of n, a(n) for n=4..89.

Andres Cicuttin, Scatter plot of first 2^13 terms

Andres Cicuttin, Fourier spectrum of first 2^16 values of the characteristic function of primes (A010051), excluding the first and last frequency components.

A. Granville and G. Martin, Prime number races, arXiv:math/0408319 [math.NT], 2004; Amer. Math. Monthly vol 113, no 1 (2006) p 1.

Example

For the first 43 terms of the characteristic function of primes (A010051), the absolute values of its discrete Fourier transform have a maximum at position 8 after excluding the smallest frequency (first position) and the largest frequency (last position), then a(43) = 8.

Mathematica

PrimeChar[n_] := If[PrimeQ[n] == True, 1, 0];
Table[Position[b = Abs@Fourier@Table[PrimeChar[j], {j, 1, n}],
   Max[b[[2 ;; Floor[n/2]]]]][[1, 1]], {n, 4, 160}]

Crossrefs

Cf. A010051, A273784, A274263, A276309.

Sequence in context: A322528 A258756 A127431 * A182921 A291268 A242767

Adjacent sequences: A289774 A289775 A289776 * A289778 A289779 A289780

Keyword

nonn

Author

Andres Cicuttin, Jul 12 2017

Status

approved