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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 Table of n, a(n) for n=1..72. 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 Adjacent sequences: A155484 A155485 A155486 * A155488 A155489 A155490 KEYWORD nonn,base AUTHOR Juri-Stepan Gerasimov, Jan 23 2009 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.)