OFFSET
1,1
COMMENTS
LINKS
Jean-François Alcover, Table of n, a(n) for n = 1..1000
EXAMPLE
a(5) = 15 because phi(15*5-1) = phi(15*5+1).
MAPLE
f:= proc(n) local k;
for k from 1 do if numtheory:-phi(k*n-1) = numtheory:-phi(k*n+1) then
return k
fi od end proc:
map(f, [$1..60]);
MATHEMATICA
kmax = 10^8;
a[n_] := For[k = 1, k <= kmax, k++, If[EulerPhi[k*n - 1] == EulerPhi[k*n + 1], Print[n, " ", k]; Return[k]]] /. Null -> -1;
Table[a[n], {n, 1, 1000}] (* Jean-François Alcover, Jun 03 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan and Robert Israel, Aug 31 2016
STATUS
approved