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
Makoto Kamada, Factorization of 77...77377...77, updated Dec 11 2018.
Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).
FORMULA
a(n) = 7*A138148(n) + 3*10^n.
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, 0]
PROG
CROSSREFS
Cf. A138148 (cyclops numbers with binary digits only).
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Feb 06 2020
STATUS
approved