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A163272
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Numbers k such that k = A074206(k), the number of ordered factorizations of k.
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10
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0, 1, 48, 1280, 2496, 28672, 29808, 454656, 2342912, 11534336, 57409536, 218103808, 34753216512, 73014444032, 583041810432, 1305670057984, 2624225017856, 404620279021568, 467515780104192, 1014849232437248, 4446425022726144, 5806013294837760, 46545625738641408
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OFFSET
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1,3
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COMMENTS
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If p is an odd prime, 2^(2*p - 2)*p belongs to the sequence, so the sequence is infinite.
If n^2 + 6*n + 6 = 2*p*q is twice the product of two distinct odd primes, 2^n*p*q belongs to the sequence.
No number of the form 2^n*p^2, with p odd prime, belongs to the sequence. (End)
For every possible prime signature (see A025487) there can be at most one number having it in this sequence. - David A. Corneth, Jul 15 2018
2*10^14 < a(18) <= 404620279021568. Also terms: 467515780104192, 1014849232437248, 4446425022726144, 5806013294837760, and 46545625738641408. - Giovanni Resta, Jul 16 2018
These numbers are named "super-perfect numbers" (Miller), "gamma-perfect numbers" (Sandor & Crstici), "factor-perfect numbers" (Knopfmacher & Mays) and "balanced numbers" (Brown). - Amiram Eldar, Aug 22 2018
Suppose one searches terms below u. We have A074206(m * t) > A074206(m) for m, t > 1 so if A074206(m) > u we needn't check any value A074206(m * t) where m * t < u.
All terms < 10^25 except 29809 are of the form 4^e * s where s is a squarefree odd number. (End)
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REFERENCES
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J. Sandor and B. Crstici, Handbook of Number Theory II, Springer, 2004, pp. 54-55.
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LINKS
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MAPLE
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A074206 := proc(n) option remember; if n <= 1 then n; else add(procname(d), d=numtheory[divisors](n) minus {n}) ; end if; end proc: for n from 1 do if n = A074206(n) then printf("%d, \n", n) ; end if; end do: \\ R. J. Mathar, Aug 01 2009
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PROG
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(PARI) term(n) = {my(f = A074206(n)); if(factor(n)[, 2] == factor(f)[, 2], f, 0) \\ returns 0 if there is no term in the sequence with prime signature of n, or if there is, returns that term. - David A. Corneth, Jul 15 2018
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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a(18)-a(23) from Amiram Eldar, Aug 22 2018, following the same suggestion with an extended list of terms of A025487.
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STATUS
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approved
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