login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A284497 a(n) is the least number such that phi(a(n)) = phi(R(a(n)))/n, where R(n) is the digit reverse of n and phi(n) is the Euler totient function of n. 2
1, 37, 12, 15, 199, 189, 124, 1004, 18, 168, 126, 12048, 10426, 1358, 11638, 1078, 1011868, 112518, 108018288, 1076768, 1012998 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(22) > 10^9. - Giovanni Resta, Mar 29 2017

LINKS

Table of n, a(n) for n=1..21.

FORMULA

Solutions of the equation A000010(n) = A000010(A004086(n))/n.

EXAMPLE

phi(1) = 1. Its digit reverse is again 1 and phi(1) = 1 = 1 * 1;

phi(37) = 36 and phi(73) = 72 = 2 * 36;

phi(12) = 4 and phi(21) = 12 = 3 * 4;

phi(15) = 8 and phi(51) = 32 = 4 * 8; etc.

MAPLE

with(numtheory): R:=proc(w) local x, y, z; x:=w; y:=0; for z from 1 to ilog10(x)+1 do y:=10*y+(x mod 10); x:=trunc(x/10); od; y; end:

P:=proc(q) local k, n; for k from 1 to q do for n from 1 to q do

if k*phi(n)=phi(R(n)) then print(n); break; fi; od; od; end: P(10^9);

MATHEMATICA

rev[n_] := FromDigits@ Reverse@ IntegerDigits@ n; a[n_] := Block[{k}, For[k = 1, EulerPhi@ rev@ k != n EulerPhi@ k, k++]; k]; Array[a, 18] (* Giovanni Resta, Mar 29 2017 *)

CROSSREFS

Cf. A000010, A004086, A284495, A284496, A284498.

Sequence in context: A107812 A254324 A068843 * A033357 A093860 A336480

Adjacent sequences:  A284494 A284495 A284496 * A284498 A284499 A284500

KEYWORD

nonn,more,base

AUTHOR

Paolo P. Lava, Mar 28 2017

EXTENSIONS

a(19)-a(21) from Giovanni Resta, Mar 29 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 19 13:55 EDT 2021. Contains 345138 sequences. (Running on oeis4.)