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A240537
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Let a(n) be the least k such that in the prime power factorization of k! the exponents of primes p_1, ...,p_n are even, while the exponent of p_(n+1) is odd.
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22
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12, 6, 10, 20, 48, 54, 338, 875, 2849, 1440, 3841, 816, 59583, 101755, 40465, 37514, 409026, 268836, 591360, 855368, 5493420, 9627251, 28953290, 14557116, 7336812, 1475128, 127632241, 531296823, 3028478192, 2435868325, 1092228841, 32377733790, 472077979
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OFFSET
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1,1
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COMMENTS
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The sequence is connected with a 1980-Erdős-Graham conjecture that, for every N, there exists an n such that in prime power factorization of n! at least N first exponents are even. In 1997, this conjecture was proved by D. Berend. A generalization was given by Y.-G. Chen (2003).
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REFERENCES
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P. Erdős, P. L. Graham, Old and new problems and results in combinatorial number theory, L'Enseignement Mathematique, Imprimerie Kunding, Geneva, 1980.
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LINKS
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PROG
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(PARI) nbe(n) = {my(f = factor(n!)[, 2], nb = 0); for (i=1, #f, if (!(f[i] % 2), nb++, break); ); nb; }
a(n) = {my(i = 1); while (nbe(i) != n, i++); i; } \\ Michel Marcus, Nov 07 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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STATUS
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approved
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