The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A239993 Numbers n such that n*sigma(n) is not divisible by 6. 0
 1, 4, 7, 9, 13, 16, 19, 25, 28, 31, 37, 43, 49, 52, 61, 64, 67, 73, 76, 79, 81, 91, 97, 100, 103, 109, 112, 121, 124, 127, 133, 139, 148, 151, 157, 163, 169, 172, 175, 181, 193, 199, 208, 211, 217, 223, 225, 229, 241, 244, 247, 256, 259, 268, 271, 277, 283, 289 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A000594(a(n)) cannot be 0 because 24 divides A000594(n) - n^4*sigma(n) for any n. LINKS MATHEMATICA Select[Range[289], ! Divisible[#*DivisorSigma[1, #], 6] &] PROG (Magma) [n: n in [1..289] | not IsZero(n*SumOfDivisors(n) mod 6)]; (PARI) for(n=1, 289, if(!Mod(n*sigma(n), 6)==0, print1(n, ", "))); CROSSREFS Supersequence of A002476. Cf. A000594. Sequence in context: A243175 A352272 A229848 * A332335 A310961 A181901 Adjacent sequences: A239990 A239991 A239992 * A239994 A239995 A239996 KEYWORD nonn AUTHOR Arkadiusz Wesolowski, Mar 30 2014 STATUS approved

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

Last modified March 23 19:52 EDT 2023. Contains 361452 sequences. (Running on oeis4.)