|
|
A291674
|
|
a(n) is the smallest k such that 2^psi(k) == 2^phi(n) (mod n).
|
|
0
|
|
|
1, 1, 3, 2, 3, 3, 2, 2, 4, 3, 19, 3, 6, 2, 3, 3, 7, 4, 10, 3, 4, 19, 43, 3, 19, 6, 10, 2, 39, 3, 19, 4, 19, 7, 6, 4, 18, 10, 6, 3, 19, 4, 13, 19, 6, 43, 137, 3, 26, 19, 7, 6, 103, 10, 19, 2, 10, 39, 173, 3, 38, 19, 4, 4, 6, 19, 86, 7, 43, 6, 139, 4, 10, 18, 19, 10, 25, 6, 206, 3, 34, 19, 163
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
COMMENTS
|
Remainders when 2^phi(n) is divided by n are 0, 0, 1, 0, 1, 4, 1, 0, 1, 6, 1, 4, 1, 8, 1, 0, 1, 10, 1, 16, 1, 12, ... (i.e., the values of "1" come from Euler's totient theorem).
If n is odd, a(n) is the least k such that psi(k) is divisible by A002326((n-1)/2). - Robert Israel, Aug 29 2017
|
|
LINKS
|
|
|
EXAMPLE
|
a(11) = 19 because 2^psi(19) == 2^phi(11) (mod 11) and 19 is the least number with this property.
|
|
MAPLE
|
N:= 1000: # to get terms before the first term > N
Psis:= Vector([$1..N]):
for p in select(isprime, [2, seq(i, i=3..N, 2)]) do
pm:= p*[$1..N/p];
Psis[pm]:= map(`*`, Psis[pm], 1+1/p);
od:
for n from 1 do
r:= 2 &^ numtheory:-phi(n) mod n;
for k from 1 to N do
if 2 &^ Psis[k] mod n = r then A[n]:= k; break fi
od:
if not assigned(A[n]) then break fi
od:
|
|
MATHEMATICA
|
psi[n_] := If[n == 1, 1, n Times @@ (1 + 1/First /@ FactorInteger@ n)]; a[n_] := Block[{k = 1, v = PowerMod[2, EulerPhi[n], n]}, While[ PowerMod[2, psi[k], n] != v, k++]; k]; Array[a, 83] (* Giovanni Resta, Aug 30 2017 *)
|
|
PROG
|
(PARI) a001615(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2] + f[i, 1]^(f[i, 2]-1));
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|