A332173 revision #3
|
| |
|
|
A332173
|
|
a(n) = 7*(10^(2n+1)-1)/9 - 4*10^n.
|
|
1
|
|
|
|
3, 737, 77377, 7773777, 777737777, 77777377777, 7777773777777, 777777737777777, 77777777377777777, 7777777773777777777, 777777777737777777777, 77777777777377777777777, 7777777777773777777777777, 777777777777737777777777777, 77777777777777377777777777777, 7777777777777773777777777777777
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
0,1
|
|
|
COMMENTS
|
According to M. Kamada, n = 0 and n = 2 are the only indices of a prime up to n = 2*10^4.
|
|
|
LINKS
|
|
|
|
FORMULA
|
G.f.: (1 + 404*x - 1100*x^2)/((1 - x)*(1 - 10*x)*(1 - 100*x)).
a(n) = 111*a(n-1) - 1110*a(n-2) + 1000*a(n-3) for n>2.
|
|
|
MAPLE
|
A332173 := n -> 7*(10^(n*2+1)-1)/9 - 4*10^n;
|
|
|
MATHEMATICA
|
Array[7 (10^(2 # + 1) - 1)/9 - 4*10^# &, 15]
|
|
|
PROG
|
(PARI) apply( {A332173(n)=10^(n*2+1)\9*7-4*10^n}, [0..15])
|
|
|
CROSSREFS
|
Cf. A138148 (cyclops numbers with binary digits only).
|
|
|
KEYWORD
|
nonn,base,easy
|
|
|
AUTHOR
|
|
|
|
STATUS
|
editing
|
| |
|
|
