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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

Table of n, a(n) for n=1..58.

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: A230240 A243175 A229848 * A310961 A181901 A310962

Adjacent sequences:  A239990 A239991 A239992 * A239994 A239995 A239996

KEYWORD

nonn

AUTHOR

Arkadiusz Wesolowski, Mar 30 2014

STATUS

approved

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Last modified November 12 19:41 EST 2019. Contains 329078 sequences. (Running on oeis4.)