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A228870 Numbers n such that 2 * (1^n + 2^n + 3^n + ... + n^n) is not 0 (mod n). 4
6, 12, 18, 20, 24, 30, 36, 40, 42, 48, 54, 60, 66, 72, 78, 80, 84, 90, 96, 100, 102, 108, 110, 114, 120, 126, 132, 138, 140, 144, 150, 156, 160, 162, 168, 174, 180, 186, 192, 198, 200, 204, 210, 216, 220, 222, 228, 234, 240, 246, 252, 258, 260, 264, 270, 272 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These are the numbers not appearing in A228869; the even numbers not in A226872.

Also, positive integers n such that there exists an odd prime divisor p of n such that (p-1) also divides n (cf. A124240). - Max Alekseyev, Sep 07 2013

This sequence agrees with A088723 for many terms, but they are different.

If n is in the sequence, then so are the multiples of n. See A280187 for primitive members of this sequence. - Charles R Greathouse IV, Dec 28 2016

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

MATHEMATICA

Select[Range[100], Mod[2*Sum[PowerMod[k, #, #], {k, #}], #] > 0 &]

PROG

(PARI) is(n)=my(f=factor(n)[, 1]); for(i=1, #f, if(n%(f[i]-1)==0 && f[i]>2, return(1))); 0 \\ Charles R Greathouse IV, Dec 28 2016

CROSSREFS

Cf. A228869, A226872.

Sequence in context: A205525 A094519 A088723 * A291022 A316221 A138939

Adjacent sequences:  A228867 A228868 A228869 * A228871 A228872 A228873

KEYWORD

nonn

AUTHOR

T. D. Noe, Sep 06 2013

STATUS

approved

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Last modified August 5 01:47 EDT 2021. Contains 346456 sequences. (Running on oeis4.)