A292005 Composite numbers k such that psi(k - phi(k)) = phi(psi(k) - k).

35, 65, 77, 161, 185, 209, 221, 335, 341, 371, 377, 437, 485, 515, 611, 671, 707, 731, 767, 779, 851, 899, 917, 965, 1007, 1067, 1115, 1157, 1211, 1247, 1271, 1337, 1385, 1397, 1529, 1535, 1577, 1631, 1691, 1781, 1817, 1841, 1991, 2117, 2171, 2201, 2285, 2291, 2327

Offset: 1

Author

Altug Alkan, Sep 07 2017

Keywords

• nonn

Comments

10217383 = 11*19^2*31*83 is the smallest term that is not squarefree.

A176875 is a subsequence.

Examples

			77 = 7*11 is a term because 77 - phi(77) = 17, psi(77) - 77 = 19 and phi(19) = psi(17).
		

Crossrefs

Cf. A000010, A001615, A176875, A290002.

Programs

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