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A163369
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a(n) = sigma(sigma(phi(n))).
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1
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1, 1, 4, 4, 8, 4, 28, 8, 28, 8, 39, 8, 56, 28, 24, 24, 32, 28, 56, 24, 56, 39, 91, 24, 96, 56, 56, 56, 120, 24, 195, 32, 96, 32, 168, 56, 112, 56, 168, 32, 234, 56, 252, 96, 168, 91, 195, 32, 252, 96, 104, 168, 171, 56, 234, 168, 112, 120, 234, 32, 480, 195
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OFFSET
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1,3
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LINKS
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FORMULA
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MAPLE
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MATHEMATICA
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DivisorSigma[1, DivisorSigma[1, EulerPhi[Range[50]]]] (* Harvey P. Dale, Jul 26 2014 *)
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PROG
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(PARI) vector(50, n, sigma(sigma(eulerphi(n)))) \\ G. C. Greubel, Dec 19 2016
(PARI) normalize(f)=if(factorback(f)==1, return(factor(1))); my(g); f=vecsort(f~)~; g=Mat(f[1, ]); for(i=2, #f~, if(f[i, 1]==g[#g~, 1], g[#g~, 2]+=f[i, 2], if(f[i, 2], g=concat(g, f[i, ])))); if(g[1, 2]==0, g[2..#g~, ], g)
expand(f)=my(g=matrix(0, 2), t); for(i=1, #f~, t=factor(f[i, 1]); for(j=1, #t~, g=concat(g, [t[j, 1], t[j, 2]*f[i, 2]]))); g
prodf(f, g)=normalize(if(factorback(f)==1, g, if(factorback(g)==1, f, concat(f~, g~)~)))
phif(f)=my(g=f); f[, 2]=apply(e->e-1, f[, 2]); g[, 1]=apply(p->p-1, g[, 1]); g[, 2]=vectorv(#g~, i, 1); prodf(expand(g), f)
sigmaf(f)=normalize(expand(matrix(#f~, 2, x, y, if(y==1, (f[x, 1]^(f[x, 2]+1)-1)/(f[x, 1]-1), 1))))
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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