A063964 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).

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

Offset: 1

Author

Jason Earls, Sep 04 2001

Keywords

• easy
• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000 (terms 1..170 from Harry J. Smith)

Crossrefs

Cf. A048250.

Programs

Mathematica

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 *)

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