OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..129
EXAMPLE
MATHEMATICA
Table[fl=1; Do[s1=DivisorSigma[1, n]/EulerPhi[n]; sk=DivisorSigma[Prime[k], n]/EulerPhi[n]; If[ !IntegerQ[s1]&&IntegerQ[sk]&&Equal[fl, 1], Print[{n, Prime[k]}]; fl=0], {n, 1, 1000000}], {k, 1, 100}]
PROG
(PARI) lista(nmax) = {my(ps = primes(nmax), pmax = ps[#ps], v = vector(pmax), c = 0, k = 2, f, e, p); while(c < nmax, f = factor(k); e = eulerphi(f); if(sigma(f) % e > 0, for(i = 1, nmax, p = ps[i]; if(!(sigma(f, p) % e) && v[p] == 0, c++; v[p] = k))); k++); for(i = 1, pmax, if(v[i] > 0, print1(v[i], ", "))); } \\ Amiram Eldar, Aug 29 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 02 2002
EXTENSIONS
a(18) corrected and more terms added by Amiram Eldar, Aug 29 2024
STATUS
approved