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Search: id:A131357
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| A131357 |
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a(1)=1, a(2)=2, for n>1 a(n)=sum of next two smallest integers >a(n-1) which are coprime to sum s=a(1)+..+a(n-1). |
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+0
1
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| 1, 2, 9, 24, 54, 120, 248, 500, 1004, 2016, 4038, 8082, 16170, 32346, 64700, 129404, 258812, 517644, 1035294, 2070594, 4141194, 8282394, 16564800, 33129608, 66259220, 132518444, 265036896, 530073798, 1060147602, 2120295210
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OFFSET
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1,2
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EXAMPLE
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n=3: a(1)=1, a(2)=2, s=1+2=3; n1=4 (not 3!) and n2=5 are both coprime to s, hence a(3)=n1+n2=9;
n=4: a(1)=1, a(2)=2, a(3)=9, s=1+2+9=12; n1=11 (not 10, 12!) and n2=13 are both coprime to s, hence a(4)=n1+n2=24;
n=5: s=36, n1=25 (not 26, 27, 28!) and n2=29 are both coprime to s, hence a(5)=n1+n2=54;
n=6: s=90; n1=59 (not 55, 56, 57, 58, 60!) and n2=61 are OK, hence a(6)=n1+n2=120.
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CROSSREFS
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Sequence in context: A101583 A006002 A023662 this_sequence A079997 A122006 A027302
Adjacent sequences: A131354 A131355 A131356 this_sequence A131358 A131359 A131360
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Sep 30 2007
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