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 A319449 Sum of the norm of divisors of n over Eisenstein integers, with associated divisors counted only once. 7
 1, 5, 13, 21, 26, 65, 64, 85, 121, 130, 122, 273, 196, 320, 338, 341, 290, 605, 400, 546, 832, 610, 530, 1105, 651, 980, 1093, 1344, 842, 1690, 1024, 1365, 1586, 1450, 1664, 2541, 1444, 2000, 2548, 2210, 1682, 4160, 1936, 2562, 3146, 2650, 2210, 4433, 3249, 3255 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Equivalent of sigma (A000203) in the ring of Eisenstein integers. Note that only norms are summed up. LINKS Jianing Song, Table of n, a(n) for n = 1..10000 Wikipedia, Eisenstein integer FORMULA Multiplicative with a(3^e) = sigma(3^(2e)) = (3^(2e+1) - 1)/2, a(p^e) = sigma(p^e)^2 = ((p^(e+1) - 1)/(p - 1))^2 if p == 1 (mod 3) and sigma_2(p^e) = A001157(p^e) = (p^(2e+2) - 1)/(p^2 - 1) if p == 2 (mod 3). EXAMPLE Let w = (1 + sqrt(3)*i)/2, w' = (1 - sqrt(3)*i)/2, and ||d|| denote the norm of d. a(3) = ||1|| + ||1 + w|| + ||3|| = 1 + 3 + 9 = 13. a(7) = ||1|| + ||2 + w|| + ||2 + w'|| + ||7|| = 1 + 7 + 7 + 49 = 64. MATHEMATICA f[p_, e_] := If[p == 3 , DivisorSigma[1, 3^(2*e)], Switch[Mod[p, 3], 1, DivisorSigma[1, p^e]^2, 2, DivisorSigma[2, p^e]]]; eisSigma[1] = 1; eisSigma[n_] := Times @@ f @@@ FactorInteger[n]; Array[eisSigma, 100] (* Amiram Eldar, Feb 10 2020 *) PROG (PARI) a(n)= { my(r=1, f=factor(n)); for(j=1, #f[, 1], my(p=f[j, 1], e=f[j, 2]); if(p==3, r*=((3^(2*e+1)-1)/2)); if(Mod(p, 3)==1, r*=((p^(e+1)-1)/(p-1))^2); if(Mod(p, 3)==2, r*=(p^(2*e+2)-1)/(p^2-1)); ); return(r); } CROSSREFS Cf. A001157. Equivalent of arithmetic functions in the ring of Eisenstein integers (the corresponding functions in the ring of integers are in the parentheses): A319442 ("d", A000005), this sequence ("sigma", A000203), A319445 ("phi", A000010), A319446 ("psi", A002322), A319443 ("omega", A001221), A319444 ("Omega", A001222), A319448 ("mu", A008683). Equivalent in the ring of Gaussian integers: A317797. Sequence in context: A190372 A184837 A197120 * A030374 A369021 A007675 Adjacent sequences: A319446 A319447 A319448 * A319450 A319451 A319452 KEYWORD nonn,mult AUTHOR Jianing Song, Sep 19 2018 STATUS approved

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Last modified August 6 03:16 EDT 2024. Contains 374957 sequences. (Running on oeis4.)