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 A365397 a(n) = 64 + A000720(n) - A365398(n). 3
 63, 63, 63, 62, 63, 62, 63, 62, 62, 61, 62, 61, 62, 62, 61, 60, 61, 60, 61, 60, 60, 60, 61, 60, 60, 60, 60, 59, 60, 59, 60, 60, 60, 60, 60, 59, 60, 60, 60, 59, 60, 59, 60, 60, 60, 60, 61, 60, 60, 60, 60, 60, 61, 60, 60, 59, 59, 59, 60, 59, 60, 60, 59, 58, 58 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS It is conjectured that A365339(n) - PrimePi(n) = 64 for all n >= 31957 (Pollack et al.). Does a similar relation apply if one replaces Euler's totient by the sum of divisors function in A365339? In particular, note remark (4.4) by Terence Tao in the linked paper. From Chai Wah Wu, Sep 08 2023: (Start) a(n) seems to be decreasing for n=10^i: a(1) = 63 a(10) = 61 a(100) = 58 a(1000) = 58 a(10^4) = 54 a(10^5) = 53 a(10^6) = 48 a(10^7) = 46 a(10^8) = 43 (End) LINKS Table of n, a(n) for n=1..65. Paul Pollack, Carl Pomerance, and Enrique Treviño, Sets of monotonicity for Euler's totient function, preprint. See M(n). Paul Pollack, Carl Pomerance, and Enrique Treviño, Sets of monotonicity for Euler's totient function, Ramanujan J. 30 (2013), no. 3, pp. 379-398. Terence Tao, Monotone non-decreasing sequences of the Euler totient function, arXiv:2309.02325 [math.NT], 2023. FORMULA a(n)<=63. This is due to the fact that A000203(p) = p+1 for p prime, and therefore A365398(n) >= A000720(n)+1. - Chai Wah Wu, Sep 08 2023 PROG (Python) from bisect import bisect from sympy import divisor_sigma, primepi def A365397(n): plist, qlist, c = tuple(divisor_sigma(i) for i in range(1, n+1)), [0]*(n+1), 0 for i in range(n): qlist[a:=bisect(qlist, plist[i], lo=1, hi=c+1, key=lambda x:plist[x])]=i c = max(c, a) return 64+primepi(n)-c # Chai Wah Wu, Sep 08 2023 CROSSREFS Cf. A000720, A000203, A365398, A365400. Sequence in context: A278827 A125638 A365400 * A332926 A112816 A296875 Adjacent sequences: A365394 A365395 A365396 * A365398 A365399 A365400 KEYWORD nonn AUTHOR Peter Luschny, Sep 08 2023 STATUS approved

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Last modified April 24 22:17 EDT 2024. Contains 371964 sequences. (Running on oeis4.)