login
A072968
Least k>0 such that the last digit of (n+k)^(n+k) is the same as the last digit of n^n.
0
10, 16, 14, 2, 10, 2, 6, 4, 10, 10, 10, 2, 14, 2, 10, 8, 6, 4, 10, 10, 10, 16, 14, 2, 10, 2, 6, 4, 10, 10, 10, 2, 14, 2, 10, 8, 6, 4, 10, 10, 10, 16, 14, 2, 10, 2, 6, 4, 10, 10, 10, 2, 14, 2, 10, 8, 6, 4, 10, 10, 10, 16, 14, 2, 10, 2, 6, 4, 10, 10, 10, 2, 14, 2, 10, 8, 6, 4, 10, 10, 10
OFFSET
1,1
LINKS
FORMULA
a(n) is periodic with period (10, 16, 14, 2, 10, 2, 6, 4, 10, 10, 10, 2, 14, 2, 10, 8, 6, 4, 10, 10, 10) of length 20
MATHEMATICA
ld[n_]:=Module[{ldn=Mod[n^n, 10], k=1}, While[Mod[(n+k)^(n+k), 10] != ldn, k++]; k]; Array[ld, 90] (* Harvey P. Dale, Sep 07 2012 *)
LinearRecurrence[{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}, {10, 16, 14, 2, 10, 2, 6, 4, 10, 10, 10, 2, 14, 2, 10, 8, 6, 4, 10, 10}, 81] (* Ray Chandler, Aug 26 2015 *)
PROG
(PARI) a(n)=if(n<0, 0, s=1; while(abs((n+s)^(n+s)%10-n^n%10)>0, s++); s)
(Python)
def a(n):
k, target = 1, pow(n, n, 10)
while pow(n+k, n+k, 10) != target: k += 1
return k
print([a(n) for n in range(1, 82)]) # Michael S. Branicky, Oct 16 2021
CROSSREFS
Sequence in context: A175335 A167788 A341012 * A072138 A109891 A104869
KEYWORD
base,easy,nonn
AUTHOR
Benoit Cloitre, Aug 13 2002
STATUS
approved