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A081324
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Twice a square but not the sum of 2 distinct squares.
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6
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0, 2, 8, 18, 32, 72, 98, 128, 162, 242, 288, 392, 512, 648, 722, 882, 968, 1058, 1152, 1458, 1568, 1922, 2048, 2178, 2592, 2888, 3528, 3698, 3872, 4232, 4418, 4608, 4802, 5832, 6272, 6498, 6962, 7688, 7938, 8192, 8712, 8978, 9522, 10082, 10368, 11552
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Conjecture: for n>1 this is A050804.
A063725(a(n)) = 1. [Reinhard Zumkeller, Aug 17 2011]
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LINKS
| Reinhard Zumkeller, Table of n, a(n) for n = 1..115, all < 10^5
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FORMULA
| Conjecture: sequence consists of numbers of form 2*k^2 such that sigma(2*k^2)==3 (mod 4) and k is not divisible by 5.
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PROG
| (Haskell)
import Data.List (elemIndices)
a081324 n = a081324_list !! (n-1)
a081324_list = 0 : elemIndices 1 a063725_list
-- Reinhard Zumkeller, Aug 17 2011
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CROSSREFS
| Cf. A050804.
Cf. A025284, A125022, A018825, A000404, A004431.
Sequence in context: A001105 A051787 A050804 * A190787 A018229 A166830
Adjacent sequences: A081321 A081322 A081323 * A081325 A081326 A081327
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KEYWORD
| nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 20 2003
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EXTENSIONS
| a(19)-a(45) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Nov 15 2009
Offset corrected by Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Aug 17 2011
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