A052465 a(n) is the smallest positive integral solution k to 24*k == 1 (mod 11^n).

6, 116, 721, 14031, 87236, 1697746, 10555551, 205427261, 1277221666, 24856698576, 154543821581, 3007660527691, 18699802411296, 363926923850606, 2262676091766811, 44035157785923321, 273783807103784126, 5328254092096721836, 33127840659557879241, 644718745143703342151, 4008468719806503388156

Offset

1,1

Comments

Related to a Ramanujan congruence for the partition function P = A000041.

Extending work of Ramanujan, Atkin (1967) proved that P(m) == 0 (mod 11^n) when 24*m == 1 (mod 11^n). In particular, P(a(n)) == 0 (mod 11^n). - Petros Hadjicostas, Jul 29 2020

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..900

A. O. L. Atkin, Proof of a Conjecture of Ramanujan, Glasgow Math. J. 8 (1967), 14-32.

G. K. Patil, Ramanujan's Life And His Contributions In The Field Of Mathematics, International Journal of Scientific Research and Engineering Studies (IJSRES), 1(6) (2014), ISSN: 2349-8862.

Eric Weisstein's World of Mathematics, Partition Function P Congruences.

Index entries for linear recurrences with constant coefficients, signature (1,121,-121).

Formula

G.f.: x*(-121*x^2 + 110*x + 6)/((1 - x)*(1 - 121*x^2)). - Vincenzo Librandi, Jul 01 2012

a(n) = a(n-1) + 121*a(n-2) - 121*a(n-3). - Vincenzo Librandi, Jul 01 2012

A000041(a(n)) == 0 (mod 11^n). - Petros Hadjicostas, Jul 29 2020

From Petros Hadjicostas, Aug 02 2020: (Start)

a(n) = (1 + 23*11^n)/24, if n is even, and a(n) = (1 + 13*11^n)/24, if n is odd.

a(n) - a(n-1) = 10*11^(n-1), if n is even >= 2, and 5*11^(n-1), if n is odd >= 3. (End)

Example

From Petros Hadjicostas, Jul 29 2020:
A000041(a(1)) = A000041(6) = 11 == 0 (mod 11^1).
A000041(a(2)) = A000041(116) = 1188908248 == 0 (mod 11^2).
A000041(a(3)) = A000041(721) = 161061755750279477635534762 == 0 (mod 11^3). (End)

Mathematica

Table[PowerMod[24, -1, 11^c], {c, 20}]
CoefficientList[Series[(-121x^2+110x+6)/((1-x)(1-121*x^2)), {x, 0, 30}], x] (* Vincenzo Librandi, Jul 01 2012 *)
LinearRecurrence[{1, 121, -121}, {6, 116, 721}, 20] (* Harvey P. Dale, Apr 27 2014 *)

Prog

(Magma) I:=[6, 116, 721]; [n le 3 select I[n] else Self(n-1)+121*Self(n-2)-121*Self(n-3): n in [1..20]]; // Vincenzo Librandi, Jul 01 2012
(PARI) a(n) = lift(Mod(24, 11^n)^-1) \\ David A. Corneth, Jul 29 2020
(SageMath)
def a(n): return 24.inverse_mod(11^n)
print([a(n) for n in range(1, 22)]) # Peter Luschny, Jul 29 2020

Crossrefs

Cf. A000041, A052462, A052463, A052466.

Sequence in context: A317172 A278752 A003425 * A229582 A113015 A362765

Adjacent sequences: A052462 A052463 A052464 * A052466 A052467 A052468

Keyword

nonn,easy

Author

Eric W. Weisstein

Extensions

More terms from David A. Corneth, Jul 29 2020

Status

approved