

A179651


Difference between consecutive practical numbers.


0



1, 2, 2, 2, 4, 4, 2, 2, 4, 4, 2, 2, 4, 4, 2, 6, 6, 2, 4, 4, 2, 6, 6, 2, 4, 4, 2, 6, 4, 4, 4, 4, 8, 6, 2, 4, 8, 4, 6, 6, 4, 2, 6, 8, 4, 12, 4, 2, 2, 4, 4, 2, 6, 4, 4, 4, 6, 6, 12, 4, 4, 4, 6, 2, 4, 4, 8, 6, 6, 4, 2, 2, 4, 8, 4, 6, 6, 4, 2, 6, 4, 8, 4, 4, 10, 2, 4, 6, 2, 4, 4, 8, 6, 2, 4, 12, 8, 8, 2, 6, 4, 2, 2
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OFFSET

1,2


COMMENTS

First occurrence of 2k, k=1..: 2, 5, 16, 33, 85, 46, 331, 188, 171, 300, 1986, 962, 3321, 968, 2316, 6514, 9974, 3219, ..., .  Robert G. Wilson v, Jul 23 2010


LINKS

Table of n, a(n) for n=1..103.


EXAMPLE

For n=3, this is 64=2.
For n=5, this is 128=4.


MATHEMATICA

PracticalQ[n_] := Module[{f, p, e, prod = 1, ok = True}, If[n < 1  (n > 1 && OddQ[n]), False, If[n == 1, True, f = FactorInteger[n]; {p, e} = Transpose[f]; Do[ If[ p[[i]] > 1 + DivisorSigma[1, prod], ok = False; Break[]]; prod = prod*p[[i]]^e[[i]], {i, Length[p]}]; ok]]]; s = Select[ Range@ 479, PracticalQ]; Rest@s  Most@s (* Robert G. Wilson v, Jul 23 2010 *)


CROSSREFS

Cf. A005153.
Sequence in context: A071472 A064135 A332476 * A139560 A192095 A105080
Adjacent sequences: A179648 A179649 A179650 * A179652 A179653 A179654


KEYWORD

easy,nonn


AUTHOR

Jason G. Wurtzel, Jul 22 2010


EXTENSIONS

a(20) onwards from Robert G. Wilson v, Jul 23 2010


STATUS

approved



