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Search: id:A057246
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| A057246 |
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s=0; d is divisor of n [here d<(n/d)]; if gcd(d,n/d)=1 or gcd(d,n/d)=d then s=s+d+(n/d); [if d=(n/d) then s=s+d] : sequence is s-n=n. See Mathematica program for more details. |
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+0
1
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OFFSET
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0,1
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EXAMPLE
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E.g. a(2)=28, gcd(1,28)=gcd(4,28/4)=1, gcd(2,28/2)=2, 1+28+4+7+2+14=56. 56-28=28.
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MATHEMATICA
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f[ n_Integer ] := (ds = Divisors[ n ]; sq = N[ Sqrt[ n ] ]; l = 1; While[ ds[[ l ] ] <= sq, l++ ]; l = l - 1; ds = Take[ ds, l ]; s = 1; k = 2; While[ k <= l, If[ GCD[ ds[[ k ] ], n/ds[[ k ] ] ] == 1 || GCD[ ds[[ k ] ], n/ds[[ k ] ] ] == ds[[ k ] ], s = s + ds[[ k ] ] + n/ds[[ k ] ] ]; k++ ]; If[ ds[[ -1 ] ] == n/ds[[ -1 ] ], s = s - d ]; s) Do[ If[ ! PrimeQ[ n ] && f[ n ] == n, Print[ n ] ], {n, 2, 33429000} ] - from Robert G. Wilson v Nov 09 2000
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CROSSREFS
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Sequence in context: A097464 A038182 A095723 this_sequence A074849 A100874 A047923
Adjacent sequences: A057243 A057244 A057245 this_sequence A057247 A057248 A057249
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KEYWORD
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more,nonn
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AUTHOR
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Naohiro Nomoto (6284968128(AT)geocities.co.jp), Sep 21 2000
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