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A077102
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Smallest m such that GCD[a+b,a-b]=n, where a=sigma[n],b=phi[n].
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2
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4, 1, 18, 21, 200, 14, 3364, 12, 722, 328, 9801, 42, 25281, 116, 1800, 15, 36992, 810, 4414201, 88, 196, 29161, 541696, 35, 2928200, 1413, 103968, 284, 98942809, 488, 1547536, 364, 19602, 17536, 814088, 370, 49042009, 55297, 1521, 440, 3150464641
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OFFSET
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1,1
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LINKS
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FORMULA
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EXAMPLE
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n=10,a(10)=328, sigma[328]=630,phi[328]=160, sigma(328)+phi(328)=790, sigma(328)-phi(328)=470, GCD[790,470]=10-n; for n=odd number, a[n] should be either a square or twice a square and so quicker search for large values is possible, like e.g. for n=97:a[97]=m=190077688441=435979^2 is the smallest solution.
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MATHEMATICA
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f[x_] := Apply[GCD, {DivisorSigma[1, x]+EulerPhi[x], DivisorSigma[1, x]-EulerPhi[x]}] t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 10^13}];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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