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A169834
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Numbers k such that d(k-1) = d(k) = d(k+1).
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7
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34, 86, 94, 142, 202, 214, 218, 231, 243, 244, 302, 375, 394, 446, 604, 634, 664, 698, 903, 922, 1042, 1106, 1138, 1262, 1275, 1310, 1335, 1346, 1402, 1642, 1762, 1833, 1838, 1886, 1894, 1925, 1942, 1982, 2014, 2055, 2102, 2134, 2182, 2218, 2265, 2306, 2344, 2362
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OFFSET
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1,1
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LINKS
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FORMULA
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MAPLE
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q:= n-> is(nops(map(numtheory[tau], {$n-1..n+1}))=1):
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MATHEMATICA
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d[n_] := DivisorSigma[0, n];
samedQ[n_] := d[n-1] == d[n] == d[n+1];
1 + Flatten@Position[Differences@#&/@Partition[DivisorSigma[0, Range@3000], 3, 1], {0, 0}] (* Hans Rudolf Widmer, Feb 02 2023 *)
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PROG
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(Haskell)
a169834 n = a169834_list !! (n-1)
a169834_list = f a051950_list [0..] where
f (0:0:ws) (x:y:zs) = y : f (0:ws) (y:zs)
f (_:v:ws) (_:y:zs) = f (v:ws) (y:zs)
(Python)
from sympy import divisor_count as d
def ok(n): return d(n-1) == d(n) == d(n+1)
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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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