login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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). 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

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 *)

PROG

(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

CROSSREFS

Cf. A048250.

Sequence in context: A195818 A101840 A061087 * A262721 A174952 A209898

Adjacent sequences:  A063961 A063962 A063963 * A063965 A063966 A063967

KEYWORD

easy,nonn

AUTHOR

Jason Earls, Sep 04 2001

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 22 22:34 EDT 2019. Contains 328335 sequences. (Running on oeis4.)