OFFSET
1,1
COMMENTS
Because Euler phi(n) = A000010(n) = A003557(n) * A173557(n), Dedekind psi(n) = A001615(n) = A003557(n) * A048250(n), and because also sigma(n) (A000203) can be computed from those three elements (see A291750), these numbers form also a subset of the positions of such duplicated occurrences of values computed for those functions. See for example A069822 and A296214.
a(11) = 61060 is the first term that is not squarefree.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..2876
EXAMPLE
PROG
(PARI)
search_up_to = (2^23);
A003557(n) = { my(f=factor(n)); for (i=1, #f~, f[i, 2] = max(0, f[i, 2]-1)); factorback(f); };
A048250(n) = if(n<1, 0, sumdiv(n, d, if(core(d)==d, d)));
A173557(n) = my(f=factor(n)[, 1]); prod(k=1, #f, f[k]-1); \\ This function from Michel Marcus, Oct 31 2017
om = Map(); m = 0; i=0; for(n = 1, search_up_to, k = Akaikki3(n); if(!mapisdefined(om, k), mapput(om, k, n), i++; write("b296087.txt", i, " ", n)));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Dec 08 2017
STATUS
approved