A291524 Numbers m such that psi(x) = phi(m) has a solution while sigma(y) = phi(m) has none.

751, 919, 1502, 1838, 2841, 3788, 5682, 6629, 8523, 11251, 11937, 13258, 13669, 14205, 15137, 15152, 15397, 15607, 15916, 16099, 17046, 18940, 19895, 22502, 22728, 23874, 27338, 28410, 30103, 30274, 30304, 30794, 31214, 31832, 32198, 36853, 37880, 39790, 43657

Offset

1,1

Comments

Values of A069825(k) such that psi(x) = phi(A069825(k)) has a solution for k > 1.

Prime terms are 751, 919, 11251, 13669, 15137, ...

Links

Table of n, a(n) for n=1..39.

Example

751 is a term because psi(x) = phi(751) = 750 has a solution that is x = 625 while there is no solution for sigma(y) = phi(751) = 750.

Prog

(PARI) is1(n) = my(N=eulerphi(n)); for(k=1, N, if(sigma(k)==N, return(1))); 0;
a001615(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2] + f[i, 1]^(f[i, 2]-1));
is2(n) = my(N=eulerphi(n)); for(k=1, N, if(a001615(k)==N, return(1))); 0;
isok(n) = !is1(n) && is2(n); \\ after Charles R Greathouse IV at A001615

Crossrefs

Cf. A000010, A000203, A001615, A069825.

Sequence in context: A015067 A129036 A290272 * A373206 A020391 A355318

Adjacent sequences: A291521 A291522 A291523 * A291525 A291526 A291527

Keyword

nonn

Author

Altug Alkan, Aug 25 2017

Status

approved