A114073 Numbers k such that phi(k) + k is a square.

5, 12, 13, 41, 44, 48, 61, 68, 108, 113, 125, 172, 176, 181, 192, 252, 268, 272, 313, 385, 421, 432, 452, 524, 613, 657, 684, 688, 704, 761, 768, 772, 825, 964, 972, 1008, 1013, 1072, 1088, 1201, 1301, 1332, 1412, 1728, 1729, 1741, 1808, 1861, 2092

Offset: 1

Author

Giovanni Resta, Feb 13 2006

Keywords

• nonn

Examples

			phi(41) + 41 = 81 = 9^2.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A121048, supersequence of A114072.

Programs

Mathematica

Select[Range[2500], IntegerQ[Sqrt[EulerPhi[#] + #]] &] (* Amiram Eldar, Jan 18 2024 *)

PARI

isok(n) = issquare(eulerphi(n) + n); \\ Michel Marcus, Jan 09 2014