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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
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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; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| 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
| a(n)=sigma(A022544(n))/4
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PROG
| (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
| Cf. A022544.
Sequence in context: A136389 A001368 A141863 * A171721 A073341 A070982
Adjacent sequences: A071007 A071008 A071009 * A071011 A071012 A071013
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KEYWORD
| easy,nonn
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AUTHOR
| Benoit Cloitre (benoit7848c(AT)orange.fr), May 19 2002
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