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Search: id:A074997
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| A074997 |
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Numbers which are sandwiched between two numbers having the same unordered canonical form. |
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+0
7
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| 4, 6, 12, 18, 19, 30, 34, 42, 51, 55, 56, 60, 72, 86, 92, 94, 102, 108, 138, 142, 144, 150, 160, 180, 184, 186, 192, 198, 202, 204, 214, 216, 218, 220, 228, 236, 240, 243, 248, 249, 266, 270, 282, 300, 302, 304, 307, 312, 320, 322, 328, 340, 341, 348, 349, 392
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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The average of twin primes is a member.
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EXAMPLE
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19 is sandwiched between 18 and 20 which are of the form p^2*q where p and q are primes.
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MAPLE
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k := 0: for j from 2 to 5000 do a := ifactors(j-1): b := ifactors(j+1): if sort([seq(a[2][i][2], i= 1..nops(a[2]))])= sort([seq(b[2][i][2], i= 1..nops(b[2]))]) then k := k+1: c[k] := j: fi: od: seq(c[i], i= 1..k);
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MATHEMATICA
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f[n_] := Flatten[Table[{ # [[2]]}] & /@ FactorInteger[n]]; Drop[ Select[ Range[415], Sort[f[ # - 1]] == Sort[f[ # + 1]] & ], 1]
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CROSSREFS
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Cf. A074998, A061715, A074460.
Sequence in context: A139056 A120453 A022802 this_sequence A045959 A072568 A109290
Adjacent sequences: A074994 A074995 A074996 this_sequence A074998 A074999 A075000
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Aug 21 2002
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EXTENSIONS
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More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de) and Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 22 2002
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