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 A261928 a(n) is the number of different pairs (x*y,x+y) mod n. 2
 1, 3, 6, 8, 15, 18, 28, 28, 36, 45, 66, 48, 91, 84, 90, 96, 153, 108, 190, 120, 168, 198, 276, 168, 275, 273, 297, 224, 435, 270, 496, 368, 396, 459, 420, 288, 703, 570, 546, 420, 861, 504, 946, 528, 540, 828, 1128, 576, 1078, 825, 918, 728, 1431, 891, 990, 784, 1140, 1305, 1770, 720, 1891, 1488, 1008, 1408, 1365, 1188, 2278 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Andrew Howroyd, Table of n, a(n) for n = 1..1000 FORMULA a(n) = n^2 - A261929(n). EXAMPLE a(2) = 3 because there exist only the pairs (0,0), (0,1) and (1,0) as results from (x*y,x+y) mod n. There are no x,y with (x*y,x+y)=(1,1) mod 2. PROG (PARI) a(n)={my(v=vector(n)); for(i=1, n, for(j=1, n, v[j]=bitor(v[j], 1<<(i*(j-i)%n)))); sum(j=1, n, hammingweight(v[j]))} \\ Andrew Howroyd, Aug 01 2018 CROSSREFS Cf. A261929 (number of other pairs). Sequence in context: A274605 A213983 A174133 * A246141 A051212 A143869 Adjacent sequences:  A261925 A261926 A261927 * A261929 A261930 A261931 KEYWORD nonn,mult AUTHOR Thomas Kerscher, Sep 06 2015 EXTENSIONS Keyword:mult added by Andrew Howroyd, Aug 01 2018 STATUS approved

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Last modified December 9 08:41 EST 2021. Contains 349627 sequences. (Running on oeis4.)