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A141847
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Least number k such that sigma2(k) >= 2^n.
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2
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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; internal format)
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OFFSET
| 1,1
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COMMENTS
| For n-bit arithmetic, m=a(n)-1 is the largest number for which sigma2(m) can be computed without overflow. For 31, 32, 63 and 64 bits, the numbers are respectively 36959, 52559, 2389186799 and 3380176799.
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..64
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FORMULA
| For large n, a(n) ~ sqrt(2) a(n-1).
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MATHEMATICA
| k=1; Table[While[DivisorSigma[2, k]<2^n, k++ ]; k, {n, 40}]
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CROSSREFS
| Cf. A001157 (sigma2).
Sequence in context: A066447 A035542 A130081 * A089333 A098492 A173508
Adjacent sequences: A141844 A141845 A141846 * A141848 A141849 A141850
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KEYWORD
| nonn
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Jul 11 2008
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