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Search: id:A071010
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| A071010 |
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Sigma(k)/4 when k is not a sum of 2 squares. |
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+0
1
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| 1, 3, 2, 3, 7, 6, 6, 5, 8, 9, 6, 15, 10, 14, 18, 8, 12, 12, 15, 14, 24, 11, 21, 18, 12, 31, 18, 30, 18, 30, 20, 15, 42, 24, 26, 36, 17, 24, 36, 18, 31, 35, 24, 42, 20, 21, 56, 33, 30, 45, 28, 42, 32, 36, 30, 63, 39, 54, 26, 48, 27, 70, 54, 38, 62, 60, 36, 45, 36, 90, 42, 56, 78
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Conjecture : if n is not the sum of 2 squares sigma(n)==0 mod 4 (converse is not true : if sigma(n)==0 mod 4 n is sometime the sum of 2 squares : sigma(65)=84==0 mod 4 but 65=49+16 is a sum of 2 squares)
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FORMULA
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a(n)=sigma(A022544(n))/4
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PROGRAM
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(PARI) for(n=0, 200, if(sum(i=0, n, sum(j=0, i, if(i^2+j^2-n, 0, 1)))==0, print1(sigma(n)/4, ", ")))
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CROSSREFS
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Cf. A022544.
Sequence in context: A136389 A001368 A141863 this_sequence A073341 A070982 A123649
Adjacent sequences: A071007 A071008 A071009 this_sequence A071011 A071012 A071013
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), May 19 2002
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