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Search: id:A109870
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| A109870 |
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Number of ways a number can be expressed as the arithmetic mean of two palindromes. |
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+0
2
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| 1, 2, 3, 4, 4, 4, 3, 2, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 4, 1, 1, 1, 1, 0, 1, 2, 2, 2, 2, 5, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 5, 2, 1, 1, 1, 2, 2, 1, 1, 1, 2, 4, 2, 1, 1, 2, 2, 2, 1, 1, 2, 2, 3, 2, 1, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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a(5)=4 because 5=(4+6)/2=(3+7)/2=(2+8)/2=(1+9)/2. a(17)=1 because 17=(1+33)/2. a(18)=1 because 18=(3+33)/2.
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MAPLE
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isA002113 := proc(n) option remember ; local digs, i ; digs := convert(n, base, 10) ; for i from 1 to nops(digs)/2 do if op(i, digs) <> op(-i, digs) then RETURN(false) ; fi ; od: RETURN(true) ; end: A109870 := proc(n) local a, d ; a := 0 ; for d from n-1 to 0 by -1 do if isA002113(d) and isA002113(2*n-d) then a := a+1 ; fi ; od: RETURN(a) ; end: seq(A109870(n), n=1..120) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 15 2007
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CROSSREFS
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Cf. A109871.
Sequence in context: A059686 A101083 A097935 this_sequence A005102 A030241 A062750
Adjacent sequences: A109867 A109868 A109869 this_sequence A109871 A109872 A109873
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jul 09 2005
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EXTENSIONS
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Corrected and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 15 2007
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