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A046694 Ramanujan tau numbers mod 691 = sum of 11th power of divisors mod 691. 10
1, 667, 252, 601, 684, 171, 531, 178, 372, 168, 469, 123, 629, 385, 309, 388, 611, 55, 672, 630, 449, 491, 92, 632, 57, 106, 88, 580, 173, 185, 366, 666, 27, 538, 429, 379, 622, 456, 269, 136, 87, 280, 36, 632, 160, 556, 435, 345, 194, 14, 570, 52, 209, 652, 172, 542, 49 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Ramanujan tau is multiplicative, so this sequence is multiplicative mod 691.

There are pairs of identical terms a(n) and a(n+1). The first such twin pair is a(184) = a(185) = 483. The indices for a first twin in a pair are listed in A121733. Corresponding twin values are listed in A121734. - Alexander Adamchuk, Aug 18 2006

Set of values of a(n) consists of all integers from 0 to 690. The first a(n) = 0 occur at n = 2*691 - 1 = 1381 that is a prime. Set of numbers n such that a(n) = 0 is a union of all terms of the arithmetic progressions k*p, where p is a prime of the form p = 2m*691 - 1 and k>0 is an integer. Primes of the form p = 2m*691 - 1 are listed in A134671 = {1381,5527,8291,12437,22111,29021,30403,...}. It appears that in a(n) there are strings of consecutive zeros of any length. The first pair of consecutive zeros occurs at n = {16581,16582}. The least numbers k such that a(n) has a string of n consecutive zeros starting with a(k) are listed in A134670(n) = {1381,16581,290217,1409635,...}. - Alexander Adamchuk, Nov 05 2007

REFERENCES

G. H. Hardy, Ramanujan: twelve lectures on subjects suggested by his life and work, AMS Chelsea Publishing, Providence, Rhode Island, 2002, p. 169, (10.6.4).

LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000

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) = A000594(n) mod A262339(6). - Jonathan Sondow, Sep 22 2015

EXAMPLE

Coefficient of x^2 in tau(x) = -24; 1^11+2^11 = 2049 = 667 mod 691 = -24 mod 691.

MAPLE

A046694 := proc(n)

    numtheory[sigma][11](n) mod 691 ;

end proc: # R. J. Mathar, Feb 01 2013

MATHEMATICA

a[n_] := Mod[Total[Divisors[n]^11], 691]; a /@ Range[57] (* Jean-Fran├žois Alcover , Apr 22 2011 *)

Table[Mod[DivisorSigma[11, n], 691], {n, 60}] (* Harvey P. Dale, Jun 01 2012 *)

PROG

(PARI) a(n)=ramanujantau(n)%691 \\ Charles R Greathouse IV, Feb 08 2017

(Python)

from sympy import divisor_sigma

def a(n): return divisor_sigma(n, 11)%691 # Indranil Ghosh, Apr 24 2017

CROSSREFS

Cf. A000594, A013959, A121733, A121734, A098108, A126812-...

Cf. also A134670, A134671, A121742, A121743, A262339.

Sequence in context: A227490 A171114 A172922 * A210477 A138563 A092797

Adjacent sequences:  A046691 A046692 A046693 * A046695 A046696 A046697

KEYWORD

easy,nice,nonn

AUTHOR

Marc LeBrun

STATUS

approved

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Last modified February 21 03:06 EST 2019. Contains 320364 sequences. (Running on oeis4.)