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A240505
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Products of primes the squares of which are Fermi-Dirac divisors of n!
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1
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1, 1, 1, 2, 2, 3, 3, 6, 2, 5, 5, 10, 10, 70, 210, 210, 210, 35, 35, 14, 14, 154, 154, 462, 2310, 30030, 10010, 715, 715, 4290, 4290, 4290, 4290, 36465, 7293, 4862, 4862, 92378, 277134, 277134, 277134, 1939938, 1939938, 88179, 146965, 6760390, 6760390, 20281170
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OFFSET
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1,4
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COMMENTS
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Or equivalently, products of primes the squares of which are infinitary divisors of n!.
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LINKS
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PROG
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(PARI) isidiv(d, f) = {if (d==1, return (1)); for (k=1, #f~, bne = binary(f[k, 2]); bde = binary(valuation(d, f[k, 1])); if (#bde < #bne, bde = concat(vector(#bne-#bde), bde)); for (j=1, #bne, if (! bne[j] && bde[j], return (0)); ); ); return (1); }
a(n) = {f = factor(n!); for (k=1, #f~, if ((f[k, 2] > 1) && isidiv(f[k, 1]^2, f), f[k, 2]=1, f[k, 2]=0); ); factorback(f); } \\ Michel Marcus, Feb 15 2016
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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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