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Search: id:A132631
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| A132631 |
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Numbers n such that sigma(n+1)-n-1 divides sigma(n)-n, where sigma(n) is sum of positive divisors of n. |
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+0
2
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| 2, 4, 6, 10, 12, 16, 18, 20, 22, 24, 28, 30, 36, 40, 42, 46, 52, 58, 60, 66, 70, 72, 78, 82, 88, 94, 96, 100, 102, 106, 108, 112, 120, 126, 130, 136, 138, 148, 150, 156, 162, 166, 172, 178, 180, 190, 192, 196, 198
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Only even numbers.
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EXAMPLE
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n=94 -> sigma(n)-n=1+2+47=50 sigma(n+1)-n-1=1+5+19=25 -> 50/25=2
n=120 -> sigma(n)-n=1+2+3+4+5+6+8+10+12+15+20+24+30+40+60=240 sigma(n+1)-n-1=1+11=12 -> 240/12=20
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MAPLE
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with(numtheory); P:=proc(n) local a, i; for i from 1 by 1 to n do if sigma(i)-i>0 then a:=(sigma(i)-i)/(sigma(i+1)-i-1); if a>0 and trunc(a)=a then print(i); fi; fi; od; end: P(200)
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CROSSREFS
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Cf. A132585, A132586, A132630.
Sequence in context: A164875 A024892 A087136 this_sequence A105965 A107304 A082417
Adjacent sequences: A132628 A132629 A132630 this_sequence A132632 A132633 A132634
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KEYWORD
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easy,nonn
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AUTHOR
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Paolo P. Lava & Giorgio Balzarotti (ppl(AT)spl.at), Aug 27 2007
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