

A320391


Numbers k such that phi(k  2) = phi(k)  2.


1



5, 7, 8, 13, 14, 16, 19, 20, 22, 31, 43, 46, 61, 64, 73, 94, 103, 109, 118, 139, 151, 166, 181, 193, 199, 214, 229, 241, 256, 271, 283, 313, 334, 349, 358, 421, 433, 454, 463, 523, 526, 571, 601, 619, 643, 661, 694, 718, 766, 811, 823, 829, 859, 883, 934, 958
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OFFSET

1,1


LINKS

Robert Israel, Table of n, a(n) for n = 1..10000


FORMULA

a(n) = A001838(n)+2.  Robert Israel, Oct 30 2018


EXAMPLE

7 is in the sequence because phi(5) = 4 = phi(7)  2.
8 is in the sequence because phi(6) = 2 = phi(8)  2.
9 is not in the sequence because phi(7) = 6 but phi(9)  2 = 4 instead.


MAPLE

with(numtheory): select(k>phi(k2)=phi(k)2, [$1..960]); # Muniru A Asiru, Oct 28 2018


MATHEMATICA

Select[Range@1000, EulerPhi@(#  2) == EulerPhi[#]  2 &]


PROG

(MAGMA) [n: n in [3..1000]  EulerPhi(n2) eq EulerPhi(n)2];
(PARI) isok(n) = eulerphi(n2) == eulerphi(n)2; \\ Michel Marcus, Oct 14 2018
(GAP) Filtered([1..960], k>Phi(k2)=Phi(k)2); # Muniru A Asiru, Oct 28 2018


CROSSREFS

Cf. A001838. Contains A006512 and terms > 10 in A194593.
Sequence in context: A257772 A314374 A066001 * A047477 A216555 A288151
Adjacent sequences: A320388 A320389 A320390 * A320392 A320393 A320394


KEYWORD

nonn


AUTHOR

Vincenzo Librandi, Oct 13 2018


STATUS

approved



