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A063964
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Numbers k such that k and k+1 have the same sum of squarefree divisors, or sqf(k) = sqf(k+1), where sqf(k) = A048250(k).
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1
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11, 14, 224, 957, 1334, 1634, 2685, 9347, 13915, 16260, 20145, 20335, 33998, 37236, 42251, 42818, 51624, 55308, 56419, 56975, 71874, 74918, 77748, 79824, 79826, 79833, 84134, 93632, 106600, 111506, 120680, 122073, 138237, 142116, 147454
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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sqs[n_] := Times@@(1 + FactorInteger[n][[;; , 1]]); seq={}; s1 = 1; Do[s2 = sqs[n]; If[s2 == s1, AppendTo[seq, n-1]]; s1 = s2, {n, 2, 10^5}]; seq (* Amiram Eldar, Aug 18 2019 *)
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PROG
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(PARI) sqf(n) = sumdiv(n, d, if(issquarefree(d), d, 0)); for(n=1, 10^7, if(sqf(n)==sqf(n+1), print(n)))
(PARI) { n=0; s=0; for (m=1, 10^9, t=sumdiv(m + 1, d, if(issquarefree(d), d, 0)); if(s==t, write("b063964.txt", n++, " ", m); if (n==170, break)); s=t ) } \\ Harry J. Smith, Sep 04 2009
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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