

A204187


Sum(m^(n1), m=1..n1) modulo n.


10



0, 1, 2, 0, 4, 3, 6, 0, 6, 5, 10, 0, 12, 7, 10, 0, 16, 9, 18, 0, 14, 11, 22, 0, 20, 13, 18, 0, 28, 15, 30, 0, 22, 17, 0, 0, 36, 19, 26, 0, 40, 21, 42, 0, 21, 23, 46, 0, 42, 25, 34, 0, 52, 27, 0, 0, 38, 29, 58, 0, 60, 31, 42, 0, 52, 33, 66, 0, 46, 35, 70, 0
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OFFSET

1,3


COMMENTS

Equals n  1 if n is 1 or a prime, by Fermat's little theorem. It is conjectured that the converse is also true; see A055032 and A201560 and note that a(n) = n1 <==> A055032(n) = 1 <==> A201560(n) = 0.  Sondow
As of 1991, Giuga and Bedocchi had verified no composite n < 10^1700 satisfies a(n) = n  1 (Ribemboim, 1991).  Alonso del Arte, May 10 2013
It seems that a(n)=n/2 iff n is of the form 4k+2.  Ivan Neretin, Sep 23 2016


REFERENCES

R. K. Guy, Unsolved Problems in Number Theory, A17.
Paulo Ribemboim, The Little Book of Big Primes. New York: SpringerVerlag (1991): 17.


LINKS

Ivan Neretin, Table of n, a(n) for n = 1..10000


FORMULA

a(p) = p  1 if p is prime, and a(4n) = 0.
a(n) + 1 == A201560(n) (mod n).


EXAMPLE

Sum(m^3, m = 1 .. 3) = 1^3 + 2^3 + 3^3 = 36 == 0 (mod 4), so a(4) = 0.


MATHEMATICA

Table[Mod[Sum[i^(n  1), {i, n  1}], n], {n, 75}] (* Alonso del Arte, May 10 2013 *)


CROSSREFS

Cf. A055023, A055030, A055031, A055032, A201560.
Cf. A191677 (zeros).
Sequence in context: A128263 A241384 A140254 * A095202 A291937 A243488
Adjacent sequences: A204184 A204185 A204186 * A204188 A204189 A204190


KEYWORD

nonn,easy


AUTHOR

Jonathan Sondow, Jan 12 2012


STATUS

approved



