OFFSET
1,1
COMMENTS
10217383 = 11*19^2*31*83 is the smallest term that is not squarefree.
A176875 is a subsequence.
EXAMPLE
77 = 7*11 is a term because 77 - phi(77) = 17, psi(77) - 77 = 19 and phi(19) = psi(17).
PROG
(PARI) a001615(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2] + f[i, 1]^(f[i, 2]-1));
isok(n) = !isprime(n) && a001615(n-eulerphi(n))==eulerphi(a001615(n)-n); \\ after Charles R Greathouse IV at A001615
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Sep 07 2017
STATUS
approved