OFFSET
1,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
MAPLE
with(numtheory): A163369:=n->sigma(sigma(phi(n))): seq(A163369(n), n=1..100); # Wesley Ivan Hurt, Dec 19 2016
MATHEMATICA
DivisorSigma[1, DivisorSigma[1, EulerPhi[Range[50]]]] (* Harvey P. Dale, Jul 26 2014 *)
PROG
(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))))
a(n)=factorback(sigmaf(sigmaf(phif(factor(n))))) \\ Charles R Greathouse IV, Dec 20 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jaroslav Krizek, Jul 25 2009
STATUS
approved