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A071601
Numbers k such that k and phi(k) have the same number of 1's in their binary representation.
1
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
1,2
LINKS
EXAMPLE
676 = 1010100100 in base 2, phi(676) = 312 = 100111000 in base 2, hence 676 is in the sequence.
MATHEMATICA
Select[Range[500], DigitCount[#, 2, 1]==DigitCount[EulerPhi[#], 2, 1]&] (* Harvey P. Dale, Jun 17 2021 *)
PROG
(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, ", ")))
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Benoit Cloitre, Jun 01 2002
STATUS
approved