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 A045769 Numbers k such that sigma(k) == 4 (mod k). 10
 1, 9, 12, 70, 88, 1888, 4030, 5830, 32128, 521728, 1848964, 8378368, 34359083008, 66072609790, 549753192448 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(16) > 10^12. - Donovan Johnson, Mar 01 2012 a(16) > 10^13. - Giovanni Resta, Apr 02 2014 a(16) > 1.5*10^14. - Jud McCranie, Jun 02 2019 a(16) <= 2251799645913088. Every number of the form 2^(j-1)*(2^j - 5), where 2^j - 5 is prime, is a term. - Jon E. Schoenfield, Jun 02 2019 LINKS MATHEMATICA Join[{1}, Select[Range[9000000], Mod[DivisorSigma[1, #], #]==4 &]] (* Harvey P. Dale, Mar 20 2011 *) PROG (PARI) is(n)=sigma(n)%n==4 || n==1 \\ Charles R Greathouse IV, Mar 09 2014 CROSSREFS Cf. A054024, A045768, A045769, A088834, A045770, A076496. Sequence in context: A341208 A328120 A072308 * A140145 A166643 A038302 Adjacent sequences:  A045766 A045767 A045768 * A045770 A045771 A045772 KEYWORD nonn AUTHOR EXTENSIONS Additional term (a(11)) from Harvey P. Dale, Mar 20 2011 Initial term 1 inserted and a(13)-a(15) from Donovan Johnson, Mar 01 2012 Typo in Mathematica program fixed by Vincenzo Librandi, Mar 11 2014 STATUS approved

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Last modified April 16 12:45 EDT 2021. Contains 343037 sequences. (Running on oeis4.)