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
Offset: 1
Keywords
Examples
13 is included because phi(14) = 6 divides phi(13) = 12.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
-
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 *)
-
PARI
lista(nn) = for (n=1, nn, if (eulerphi(n) % eulerphi(n+1) == 0, print1(n, ", "))); \\ Michel Marcus, Sep 14 2015
Comments