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A336917
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Number of iterations of x -> A252463(x) needed before the result is deficient, when starting from x=n.
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2
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0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 3, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 1, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 1, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 3, 0, 0, 0, 0, 0, 1, 0, 3, 0, 0, 0, 2, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 5, 0, 0, 0, 1, 0, 1, 0, 1, 0
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OFFSET
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1,12
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LINKS
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FORMULA
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EXAMPLE
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For n = 945, the first odd abundant number, the iteration of A252463 proceeds as 945 -> 120 -> 60 -> 30 -> 15 -> 6 -> 3 -> 2 -> 1. From 945 to 30, all are nondeficient (sigma(k) >= 2k), and only at 15 we encounter the first deficient number, as sigma(15) = 24 < 2*15. Therefore a(945) = 4.
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PROG
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(PARI)
A064989(n) = {my(f); f = factor(n); if((n>1 && f[1, 1]==2), f[1, 2] = 0); for (i=1, #f~, f[i, 1] = precprime(f[i, 1]-1)); factorback(f)};
A336917(n) = { my(i=0); while(sigma(n) >= (2*n), n = A252463(n); i++); (i); };
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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