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A121315
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Products of two consecutive prime powers.
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1
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2, 6, 12, 20, 35, 56, 72, 99, 143, 208, 272, 323, 437, 575, 675, 783, 899, 992, 1184, 1517, 1763, 2021, 2303, 2597, 3127, 3599, 3904, 4288, 4757, 5183, 5767, 6399, 6723, 7387, 8633, 9797, 10403, 11021, 11663, 12317, 13673, 15125, 15875, 16256, 16768
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| For some algorithms for finding A034699(n), the numbers in this sequence represent a worst case scenario of execution time.
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FORMULA
| a(n) = A000961(n)*A000961(n+1)
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EXAMPLE
| 437 = 19*23 and none of the intervening integers (20,21,22) are prime powers.
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MATHEMATICA
| t = Join[{1}, Select[Range[2, 131], Mod[ #, # - EulerPhi[ # ]] == 0 &]]; Most@t*Rest@t - Robert G. Wilson v, Sept 02 2006
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CROSSREFS
| Cf. A000961, A034699.
Sequence in context: A194110 A184432 A003274 * A078878 A095361 A095362
Adjacent sequences: A121312 A121313 A121314 * A121316 A121317 A121318
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KEYWORD
| nonn
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AUTHOR
| Paul Richards (pr(AT)paulrichards.me.uk), Aug 28 2006
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EXTENSIONS
| More terms from Robert G. Wilson v, Sept 02 2006
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