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A155487 Difference between n-th composite number and twice its least prime factor. 0
0, 2, 4, 3, 6, 8, 10, 9, 12, 14, 16, 15, 18, 20, 15, 22, 21, 24, 26, 28, 27, 30, 25, 32, 34, 33, 36, 38, 40, 39, 42, 44, 35, 46, 45, 48, 50, 45, 52, 51, 54, 56, 58, 57, 60, 55, 62, 64, 63, 66, 68, 70, 69, 72, 63, 74, 76, 75, 78, 80, 75, 82, 81, 84, 86, 77, 88, 87, 90, 85, 92, 94 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
EXAMPLE
1st composite is 4 = 2^2; lpf = 2, so a(1) = 4 - 2*2 = 0;
2nd composite is 6 = 2*3; lpf = 2, so a(2) = 6 - 2*2 = 2;
3rd composite is 8 = 2^3; lpf = 2, so a(3) = 8 - 2*2 = 4;
4th composite is 9 = 3^2; lpf = 3, so a(4) = 9 - 2*3 = 3;
5th composite is 10 = 2*5; lpf = 2, so a(5) = 10 - 2*2 = 6.
MATHEMATICA
#-2*FactorInteger[#][[1, 1]]&/@Select[Range[200], CompositeQ] (* Harvey P. Dale, Mar 29 2020 *)
CROSSREFS
Cf. A002808.
Sequence in context: A120241 A352714 A355435 * A356430 A128555 A039874
KEYWORD
nonn,base
AUTHOR
EXTENSIONS
Entries checked by R. J. Mathar, May 10 2010
STATUS
approved

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Last modified April 12 22:48 EDT 2024. Contains 371639 sequences. (Running on oeis4.)