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A087786 a(n) = number of solutions to x^3 - y^3 == 0 (mod n). 6
1, 2, 3, 6, 5, 6, 19, 20, 27, 10, 11, 18, 37, 38, 15, 40, 17, 54, 55, 30, 57, 22, 23, 60, 45, 74, 135, 114, 29, 30, 91, 112, 33, 34, 95, 162, 109, 110, 111, 100, 41, 114, 127, 66, 135, 46, 47, 120, 175, 90, 51, 222, 53, 270, 55, 380, 165, 58, 59, 90, 181, 182, 513, 352, 185 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..10000

FORMULA

Multiplicative with a(p^e) = p^(2*floor(2*e/3)) + Sum_{i=0..floor((e-1)/3)} k*(p-1)*p^(e+i-1) where k = 3 if (p = 3 and 3*i+1 = e) or (p mod 3 = 1) otherwise k = 1. - Andrew Howroyd, Jul 17 2018

PROG

(PARI) a(n)={my(v=vector(n)); for(i=0, n-1, v[i^3%n + 1]++); sum(i=0, n-1, v[i+1]^2)} \\ Andrew Howroyd, Jul 17 2018

(PARI) a(n)={my(f=factor(n)); prod(i=1, #f~, my(p=f[i, 1], e=f[i, 2]); p^(2*(2*e\3)) + sum(i=0, (e-1)\3, if(p%3==1 || (p==3&&3*i<e-1), 3, 1)*(p-1)*p^(e+i-1)) )} \\ Andrew Howroyd, Jul 17 2018

CROSSREFS

Cf. A046530, A087694, A062803.

Sequence in context: A242311 A097723 A187831 * A210468 A080950 A023852

Adjacent sequences:  A087783 A087784 A087785 * A087787 A087788 A087789

KEYWORD

mult,nonn

AUTHOR

Yuval Dekel (dekelyuval(AT)hotmail.com), Oct 06 2003

EXTENSIONS

More terms from John W. Layman, Oct 18 2003

STATUS

approved

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Last modified February 15 16:53 EST 2019. Contains 320136 sequences. (Running on oeis4.)