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A067172 Numbers k such that sigma(k-2) + sigma(k+2) = sigma(2k). 1
4, 16, 272, 284, 604, 4556, 6904, 8413, 10463, 12070, 19004, 23290, 26284, 29944, 40312, 44252, 107557, 114616, 230987, 239134, 276476, 332022, 343793, 403196, 501008, 762078, 771130, 893606, 1013348, 1160192, 1731290, 1807016, 2066404 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
MATHEMATICA
Select[Range[10^6], DivisorSigma[1, #-2] + DivisorSigma[1, #+2] == DivisorSigma[1, 2*#] &] (* Amiram Eldar, May 13 2022 *)
PROG
(PARI) s1=1; s2=3; s3=4; s4=7; for(n=3, 10^9, s5=sigma(n+2); if(s1+s5==sigma(2*n), print(n)); s1=s2; s2=s3; s3=s4; s4=s5) \\ Donovan Johnson, Sep 17 2013
CROSSREFS
Sequence in context: A212297 A152153 A144988 * A013089 A203105 A273474
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 18 2002
EXTENSIONS
a(19)-a(33) from Donovan Johnson, Jan 31 2009
STATUS
approved

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Last modified March 29 11:14 EDT 2024. Contains 371278 sequences. (Running on oeis4.)