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A260905
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Totients of the Blum integers.
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1
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12, 20, 36, 44, 60, 60, 84, 108, 92, 132, 116, 132, 180, 140, 180, 156, 164, 220, 252, 204, 212, 276, 300, 252, 260, 348, 276, 396, 300, 396, 420, 324, 420, 332, 460, 356, 468, 380, 492, 540, 396, 420, 580, 444, 452, 660, 476, 612, 660, 636, 500, 700, 524
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = phi(Blum(n)) = A000010(A016105(n)), where phi(n) is Euler's totient function and Blum(n) is the n-th Blum integer.
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EXAMPLE
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For the first Blum integer, a(1) = phi(21) = 12.
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MAPLE
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N:= 1000: # to get all terms <= N
Primes:= select(isprime, [seq(4*i+3, i=0.. floor(N/12 - 3/4))]):
Pairs:= select(t -> t[1]*t[2]<=N, [seq(seq([Primes[i], Primes[j]], j=i+1..nops(Primes)), i=1..nops(Primes))]):
map(t -> (t[1]-1)*(t[2]-1), sort(Pairs, (s, t) -> s[1]*s[2] < t[1]*t[2])); # Robert Israel, Nov 18 2015
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MATHEMATICA
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EulerPhi@ With[{lim = 820}, Select[Union[Times @@@ Subsets[Select[Prime@ Range@ PrimePi@ NextPrime[lim/3], Mod[#, 4] == 3 &], {2}]], # <= lim &]] (* Michael De Vlieger, Nov 18 2015, after Harvey P. Dale at A016105 *)
EulerPhi[Select[4Range[5, 197] + 1, PrimeNu[#] == 2 && MoebiusMu[#] == 1 && Mod[FactorInteger[#][[1, 1]], 4] != 1 &]] (* Alonso del Arte, Nov 18 2015 *)
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PROG
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(Perl) use ntheory ":all"; forcomposites { say euler_phi($_) if ($_ % 4) == 1 && is_square_free($_) && scalar(factor($_)) == 2 && !scalar(grep { ($_ % 4) != 3 } factor($_)); } 1000; # Dana Jacobsen, Dec 10 2015
(Python)
from sympy import factorint, totient
def isBlum(n):
fn = factorint(n)
return len(fn) == sum(fn.values()) == 2 and all(f%4 == 3 for f in fn)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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