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 A141847 Least number k such that sigma_2(k) >= 2^n. 2
 2, 2, 3, 4, 6, 8, 10, 15, 20, 28, 40, 54, 78, 108, 156, 216, 300, 420, 600, 840, 1188, 1680, 2340, 3360, 4680, 6600, 9240, 13200, 18480, 26400, 36960, 52560, 73920, 105000, 147840, 209160, 294840, 415800, 589680, 831600, 1178100, 1663200, 2353680 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For n-bit arithmetic, m=a(n) - 1 is the largest number for which sigma_2(m) can be computed without overflow. For 31, 32, 63 and 64 bits, the numbers are respectively 36959, 52559, 2389186799 and 3380176799. LINKS T. D. Noe, Table of n, a(n) for n=1..64 FORMULA For large n, a(n) ~ sqrt(2)*a(n-1). MATHEMATICA k=1; Table[While[DivisorSigma[2, k]<2^n, k++ ]; k, {n, 40}] CROSSREFS Cf. A001157 (sigma_2). Sequence in context: A035542 A225484 A130081 * A182372 A089333 A098492 Adjacent sequences: A141844 A141845 A141846 * A141848 A141849 A141850 KEYWORD nonn AUTHOR T. D. Noe, Jul 11 2008 STATUS approved

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Last modified May 30 12:57 EDT 2023. Contains 363050 sequences. (Running on oeis4.)