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A055020
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Number of iterations of sigma() required until 2n (or greater) is reached.
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5
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2, 2, 2, 2, 1, 2, 2, 3, 2, 2, 1, 3, 2, 2, 2, 2, 1, 2, 1, 2, 2, 2, 1, 3, 2, 2, 1, 2, 1, 2, 2, 2, 2, 2, 1, 3, 2, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 2, 2, 1, 2, 1, 2, 2, 2, 1, 3, 2, 2, 2, 2, 1, 3, 2, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 2, 1, 4, 2, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 2, 2, 2, 1, 3, 2, 2, 1, 2, 1, 2, 1
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OFFSET
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2,1
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LINKS
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EXAMPLE
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sigma(sigma(sigma(9))) = 24 >= 2*9, so a(9) = 3.
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MATHEMATICA
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a[n_] := -1 + Length@ NestWhileList[DivisorSigma[1, #] &, n, # < 2*n &]; Array[a, 100, 2] (* Amiram Eldar, Mar 18 2024 *)
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PROG
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(PARI) a(n) = {my(m = n, nn = 2*n, c = 0); while(m < nn, m = sigma(m); c++); c; } \\ Amiram Eldar, Mar 18 2024
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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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