A228870 Numbers n such that 2 * (1^n + 2^n + 3^n + ... + n^n) is not 0 (mod n).

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

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 A348719 A316221

Adjacent sequences: A228867 A228868 A228869 * A228871 A228872 A228873

Keyword

nonn

Author

T. D. Noe, Sep 06 2013

Status

approved