A189510 Digital root of n^n.

1, 1, 4, 9, 4, 2, 9, 7, 1, 9, 1, 5, 9, 4, 7, 9, 7, 8, 9, 1, 4, 9, 4, 2, 9, 7, 1, 9, 1, 5, 9, 4, 7, 9, 7, 8, 9, 1, 4, 9, 4, 2, 9, 7, 1, 9, 1, 5, 9, 4, 7, 9, 7, 8, 9, 1, 4, 9, 4, 2, 9, 7, 1, 9, 1, 5, 9, 4, 7, 9, 7, 8, 9, 1, 4, 9, 4, 2, 9, 7, 1, 9, 1, 5, 9, 4, 7

Offset

0,3

Comments

a(n) = A010888(A000312(n)).

For n >= 1, this sequence is periodic with period 18. The sequence repeats [1,4,9,4,2,9,7,1,9,1,5,9,4,7,9,7,8,9]. - Nathaniel Johnston, May 04 2011

Links

Table of n, a(n) for n=0..86.

Index entries for linear recurrences with constant coefficients, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1).

Formula

From Chai Wah Wu, Feb 09 2023: (Start)

a(n) = a(n-18) for n > 18.

G.f.: (-8*x^18 - 8*x^17 - 7*x^16 - 9*x^15 - 7*x^14 - 4*x^13 - 9*x^12 - 5*x^11 - x^10 - 9*x^9 - x^8 - 7*x^7 - 9*x^6 - 2*x^5 - 4*x^4 - 9*x^3 - 4*x^2 - x - 1)/(x^18 - 1). (End)

Maple

A189510 := proc(n) return ((n^n-1) mod 9) + 1: end: seq(A189510(n), n=0..80); # Nathaniel Johnston, May 04 2011

Mathematica

digitalRoot[n_Integer?Positive] := FixedPoint[Plus@@IntegerDigits[#]&, n]; Table[If[n==0, 0, digitalRoot[n^n]], {n, 0, 200}]
Join[{1}, LinearRecurrence[{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}, {1, 4, 9, 4, 2, 9, 7, 1, 9, 1, 5, 9, 4, 7, 9, 7, 8, 9}, 86]] (* Ray Chandler, Aug 27 2015 *)

Prog

(Python)
def A189510(n): return (9, 1, 4, 9, 4, 2, 9, 7, 1, 9, 1, 5, 9, 4, 7, 9, 7, 8)[n%18] if n else 1 # Chai Wah Wu, Feb 09 2023

Crossrefs

Cf. A010888, A030132, A145389.

Sequence in context: A244994 A021091 A096415 * A341953 A341767 A281152

Adjacent sequences: A189507 A189508 A189509 * A189511 A189512 A189513

Keyword

nonn,base,easy

Author

Vladimir Joseph Stephan Orlovsky, May 02 2011

Extensions

a(0) corrected by Reinhard Zumkeller, May 03 2011

Status

approved