|
|
A087271
|
|
Least number x such that gcd(x, pi(x)) = n.
|
|
0
|
|
|
1, 4, 6, 8, 50, 66, 77, 56, 27, 30, 33, 156, 169, 182, 465, 224, 238, 252, 2299, 1380, 189, 902, 207, 96, 100, 1872, 1323, 2464, 1247, 120, 1333, 3168, 528, 1258, 1295, 828, 3441, 2888, 1755, 5800, 1271, 1932, 731, 748, 765, 2852, 2209, 11568, 2695, 4000
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
LINKS
|
|
|
FORMULA
|
a(n) = Min{x; gcd(x, A000720(x))=n}.
|
|
EXAMPLE
|
n=253: a(253)=91586, pi(91586)=8855,
gcd(91586, 8855) = 253 first time.
|
|
MATHEMATICA
|
f[x_] := GCD[x, PrimePi[x]]; t=Table[0, {257}]; Do[s=f[n]; If[s<258&&t[[s]]==0, t[[s]]=n], {n, 1, 100000}]; t
Module[{tbl=Table[{x, GCD[x, PrimePi[x]]}, {x, 12000}]}, Table[SelectFirst[ tbl, #[[2]]==n&], {n, 50}]][[All, 1]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Feb 12 2020 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|