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A152000
a(n) is squarefree and such that for every prime p|a(n) and every prime q|p-1 then q|a(n) holds.
2
2, 6, 10, 30, 34, 42, 78, 102, 110, 114, 170, 210, 222, 330, 390, 410, 438, 510, 514, 546, 570, 582, 654, 714, 798, 930, 978, 1010, 1110, 1158, 1218, 1230, 1326, 1482, 1542, 1554, 1806, 1830, 1870, 1938, 2190, 2310, 2510, 2530
OFFSET
1,1
COMMENTS
a(n) is a squarefree valid base.
Numbers m > 1 such that m equals A007947(A002618(m)). - Jon Maiga, Aug 08 2019
LINKS
J. Jimenez Urroz and J. Luis A.Yebra, On the equation a^x=x mod b^n, Journal of Integer Sequences, Vol. 12 (2009), Article 09.8.8.
MAPLE
A152000 := proc(n)
if n = 1 then
2;
else
for a from procname(n-1)+1 do
if issqrfree(a) then
pdvs := numtheory[factorset](a) ;
aworks := true;
for p in numtheory[factorset](a) do
for q in numtheory[factorset](p-1) do
if a mod q = 0 then
;
else
aworks := false;
end if;
end do:
end do:
if aworks then
return a;
end if;
end if;
end do:
end if;
end proc: # R. J. Mathar, Jun 01 2013
MATHEMATICA
rad[n_] := Times @@ (First@# & /@ FactorInteger@n);
Select[Range[2, 2530], # == rad[#*EulerPhi[#]] &] (* Jon Maiga, Aug 08 2019 *)
PROG
(PARI) is(m) = factorback(factorint(m*eulerphi(m))[, 1]) == m && m > 1; \\ Jinyuan Wang, Aug 08 2019
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
J. Luis, A. Yebra and J. Jimenez Urroz, Nov 19 2008
EXTENSIONS
Corrected and extended by Michel Marcus, Jun 01 2013
STATUS
approved