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 A038698 Surfeit of 4k-1 primes over 4k+1 primes, beginning with prime 2. 28
 0, 1, 0, 1, 2, 1, 0, 1, 2, 1, 2, 1, 0, 1, 2, 1, 2, 1, 2, 3, 2, 3, 4, 3, 2, 1, 2, 3, 2, 1, 2, 3, 2, 3, 2, 3, 2, 3, 4, 3, 4, 3, 4, 3, 2, 3, 4, 5, 6, 5, 4, 5, 4, 5, 4, 5, 4, 5, 4, 3, 4, 3, 4, 5, 4, 3, 4, 3, 4, 3, 2, 3, 4, 3, 4, 5, 4, 3, 2, 1, 2, 1, 2, 1, 2, 3, 2, 1, 0, 1, 2, 3, 4, 5, 6, 7, 6, 5, 6, 5, 6, 5, 6, 5, 6 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS a(n) < 0 for infinitely many values of n. - Benoit Cloitre, Jun 24 2002 First negative value is a(2946) = -1, which is for prime 26861. - David W. Wilson, Sep 27 2002 The elements of this sequence can be found in the Discrete Fourier Transform X[f] of length 4N on the prime number sequence x[n] from n=0 to 4N-1, where x[n] = 1 when n is prime otherwise x[n] is zero. The complex Fourier components of the n-th harmonic equals the complex number X[N] = -1 + j[pi(4k+1) - pi(4k-1)], where pi(4k+1) and pi(4k-1) are the number of primes of the form 4k+1 and 4k-1 less than 4N respectively. - Paul Mackenzie (paul.mackenzie(AT)ozemail.com.au), Jul 09 2010 REFERENCES Stan Wagon, The Power of Visualization, Front Range Press, 1994, p. 2. LINKS T. D. Noe and N. J. A. Sloane, Table of n, a(n) for n = 1..20000, Jun 24 2016 [First 10000 terms from T. D. Noe] FORMULA a(n) = Sum_{k=2..n} (-1)^((prime(k)+1)/2). - Benoit Cloitre, Jun 24 2002 a(n) = (Sum_{k=1..n} prime(k) mod 4) - 2n. (Assuming that x mod 4 is a positive number.) - Thomas Ordowski, Sep 21 2012 From Antti Karttunen, Oct 01 2017: (Start) a(n) = A267098(n) - A267097(n). a(n) = A292378(A000040(n)). (End) MAPLE ans:=; ct:=0; for n from 2 to 2000 do p:=ithprime(n); if (p mod 4) = 3 then ct:=ct+1; else ct:=ct-1; fi; ans:=[op(ans), ct]; od: ans; # N. J. A. Sloane, Jun 24 2016 MATHEMATICA FoldList[Plus, 0, Mod[Prime[Range[2, 110]], 4] - 2] Join[{0}, Accumulate[If[Mod[#, 4]==3, 1, -1]&/@Prime[Range[2, 110]]]] (* Harvey P. Dale, Apr 27 2013 *) PROG (PARI) for(n=2, 100, print1(sum(i=2, n, (-1)^((prime(i)+1)/2)), ", ")) CROSSREFS Cf. A007350, A007351, A038691, A066520. Cf. A112632 (race of 3k-1 and 3k+1 primes), A216057, A269364. Cf. A156749 (sequence showing Chebyshev bias in prime races (mod 4)), A199547, A267097, A267098, A267107, A292378. Sequence in context: A241062 A333471 A284620 * A333590 A263233 A300623 Adjacent sequences:  A038695 A038696 A038697 * A038699 A038700 A038701 KEYWORD sign,easy,nice,hear AUTHOR STATUS approved

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Last modified October 2 19:31 EDT 2022. Contains 357228 sequences. (Running on oeis4.)