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A126828 Ramanujan numbers (A000594) read mod 81. 0
1, 57, 9, 67, 51, 27, 23, 78, 0, 72, 12, 36, 35, 15, 54, 70, 45, 0, 38, 15, 45, 36, 69, 54, 61, 51, 0, 2, 3, 0, 17, 9, 27, 54, 39, 0, 74, 60, 72, 9, 6, 54, 41, 75, 0, 45, 75, 63, 21, 75, 0, 77, 54, 0, 45, 12, 18, 9, 24, 54, 50, 78, 0, 37, 3, 0, 62, 18, 54, 36, 18, 0, 65, 6, 63, 35, 33, 54 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..78.

R. P. Bambah and S. Chowla, Congruence properties of Ramanujan’s function tau(n), Bull. Amer. Math. Soc. 53 (1947), 950-955.

H. P. F. Swinnerton-Dyer, On l-adic representations and congruences for coefficients of modular forms, pp. 1-55 of Modular Functions of One Variable III (Antwerp 1972), Lect. Notes Math., 350, 1973.

FORMULA

a(n) = (n^2+k)*sigma_7(n) with k=0 if gcd(n,3)=1 and k=9 if gcd(n,3)=2. - Michel Marcus, Apr 26 2016

MATHEMATICA

Mod[RamanujanTau@ #, 81] & /@ Range@ 78 (* Michael De Vlieger, Apr 26 2016 *)

CROSSREFS

Cf. A000594, A013955.

Sequence in context: A244190 A013682 A278068 * A241310 A033377 A291496

Adjacent sequences:  A126825 A126826 A126827 * A126829 A126830 A126831

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Feb 25 2007

STATUS

approved

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Last modified July 12 21:31 EDT 2020. Contains 335669 sequences. (Running on oeis4.)