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A214932 Number of practical numbers between powers of 2 where the practical numbers b(k) are A005153. 0
1, 1, 2, 2, 6, 8, 15, 25, 52, 89, 166, 299, 551, 1050, 1954, 3737, 7098, 13423, 25262, 48028, 91636, 175204, 334986, 643526, 1240052, 2394026 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

a(n) appears to be a complete sequence analogous to A036378.

LINKS

Table of n, a(n) for n=0..25.

EXAMPLE

a(4)=6 as there are 4 practical numbers > 16 and <= 32 namely 18, 20, 24, 28, 30 and 32.

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]]]; Table[Length[Select[Range[2^n + 1, 2^(n + 1)], PracticalQ]],

  {n, 0, 25}](* using T. D. Noe's program A005153 *)

CROSSREFS

Cf. A005153, A036378.

Sequence in context: A248823 A284616 A136513 * A322132 A054153 A000673

Adjacent sequences:  A214929 A214930 A214931 * A214933 A214934 A214935

KEYWORD

nonn,more

AUTHOR

Frank M Jackson, May 03 2013

STATUS

approved

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Last modified September 27 03:21 EDT 2020. Contains 337380 sequences. (Running on oeis4.)