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 A065358 The Jacob's Ladder sequence: a(n) = Sum_{k=1..n} (-1)^pi(k), where pi = A000720. 11
 0, 1, 0, 1, 2, 1, 0, 1, 2, 3, 4, 3, 2, 3, 4, 5, 6, 5, 4, 5, 6, 7, 8, 7, 6, 5, 4, 3, 2, 3, 4, 3, 2, 1, 0, -1, -2, -1, 0, 1, 2, 1, 0, 1, 2, 3, 4, 3, 2, 1, 0, -1, -2, -1, 0, 1, 2, 3, 4, 3, 2, 3, 4, 5, 6, 7, 8, 7, 6, 5, 4, 5, 6, 5, 4, 3, 2, 1, 0, 1, 2, 3, 4, 3, 2, 1, 0, -1, -2, -1, 0, 1, 2, 3, 4, 5, 6, 5, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Partial sums of A065357. LINKS N. J. A. Sloane, Table of n, a(n) for n = 0..10000 (First 1000 terms from Harry J. Smith.) Theophilus Agama, The prime index function, arXiv:1905.03112 [math.GM], 2019. Alberto Fraile, Roberto MartÃ­nez, and Daniel FernÃ¡ndez, Jacob's Ladder: Prime numbers in 2d, arXiv preprint arXiv:1801.01540 [math.HO], 2017. Also Prime Numbers in 2D, Math. Comput. Appl. 2020, 25, 5; https://www.mdpi.com/2297-8747/25/1/5 [They describe essentially this sequence except with offset 1 instead of 0 - N. J. A. Sloane, Feb 20 2018] Hans Havermann, Graph of first 30 million terms. [As can seen from A064940, one has to go out beyond 44 million terms to see any further runs of positive terms.] MAPLE with(numtheory): f:=n->add((-1)^pi(k), k=1..n); [seq(f(n), n=0..60)]; # N. J. A. Sloane, Feb 20 2018 MATHEMATICA Table[Sum[(-1)^(PrimePi[k]), {k, 1, n}], {n, 0, 100}] (* G. C. Greubel, Feb 20 2018 *) a[0] = 0; a[n_] := a[n] = a[n - 1] + (-1)^PrimePi[n]; Array[a, 105, 0] (* Robert G. Wilson v, Feb 20 2018 *) PROG (PARI) { a=0; for (n=1, 1000, a+=(-1)^primepi(n); write("b065358.txt", n, " ", a) ) } \\ Harry J. Smith, Sep 30 2009 [0] cat [(&+[(-1)^(#PrimesUpTo(k)):k in [1..n]]): n in [1..100]];  // G. C. Greubel, Feb 20 2018 CROSSREFS Cf. A000720, A065357, A064940 (the zero terms). Sequence in context: A053646 A080776 A297158 * A062329 A022958 A023444 Adjacent sequences:  A065355 A065356 A065357 * A065359 A065360 A065361 KEYWORD easy,sign,nice AUTHOR Jason Earls, Oct 31 2001 EXTENSIONS Edited by Frank Ellermann, Feb 02 2002 Edited by N. J. A. Sloane, Feb 20 2018 (added initial term a(0)=0, added name suggested by the Fraile et al. paper) STATUS approved

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Last modified July 24 02:31 EDT 2021. Contains 346270 sequences. (Running on oeis4.)