A071601 Numbers k such that k and phi(k) have the same number of 1's in their binary representation.

1, 2, 4, 8, 9, 16, 18, 32, 33, 36, 49, 64, 65, 66, 69, 72, 77, 98, 99, 121, 128, 130, 132, 138, 141, 144, 145, 154, 169, 177, 196, 198, 209, 225, 242, 256, 260, 261, 264, 265, 276, 282, 288, 290, 297, 305, 308, 325, 338, 354, 361, 392, 396, 418, 441, 450, 484

Offset: 1

Author

Benoit Cloitre, Jun 01 2002

Keywords

• base
• easy
• nonn

Examples

			676 = 1010100100 in base 2, phi(676) = 312 = 100111000 in base 2, hence 676 is in the sequence.
		

Links

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

Crossrefs

Cf. A000010, A000120, A295660.

Programs

Mathematica

Select[Range[500],DigitCount[#,2,1]==DigitCount[EulerPhi[#],2,1]&] (* Harvey P. Dale, Jun 17 2021 *)

PARI

for(n=1,1000,if(sum(i=1,length(binary(n)), component(binary(n),i))==sum(i=1,length(binary(eulerphi(n))), component(binary(eulerphi(n)),i)),print1(n,",")))