A057920 - OEIS

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A057920

Numbers k such that phi(k+1) divides phi(k), where phi is A000010.

1, 3, 5, 13, 15, 35, 37, 61, 73, 104, 119, 157, 164, 193, 194, 255, 277, 313, 397, 421, 455, 457, 495, 527, 541, 545, 584, 613, 629, 661, 665, 673, 733, 757, 877, 975, 997, 1085, 1093, 1153, 1201, 1213, 1237, 1295, 1321, 1381, 1453, 1469, 1621, 1657, 1753

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

The intersection of this sequence and A057919 is A001274. - Michel Marcus, Sep 14 2015

LINKS

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

EXAMPLE

13 is included because phi(14) = 6 divides phi(13) = 12.

MAPLE

for n from 1 to 2000 do

if modp(numtheory[phi](n), numtheory[phi](n+1)) =0 then

printf("%d, ", n) ;

end if;

end do: # R. J. Mathar, Sep 14 2015

MATHEMATICA

Select[Range[1800], Divisible[EulerPhi[#], EulerPhi[# + 1]] &] (* Amiram Eldar, Jul 13 2019 *)

PROG

(PARI) lista(nn) = for (n=1, nn, if (eulerphi(n) % eulerphi(n+1) == 0, print1(n, ", "))); \\ Michel Marcus, Sep 14 2015

CROSSREFS

Cf. A001274, A057919.

Sequence in context: A018753 A073217 A063484 * A018329 A090545 A045411

Adjacent sequences: A057917 A057918 A057919 * A057921 A057922 A057923

KEYWORD

nonn

AUTHOR

Leroy Quet, Nov 11 2000

STATUS

approved