OFFSET
0,1
COMMENTS
See A183179 = {2, 3, 6, 23, 36, 69, 561, ...} for the indices of primes.
LINKS
Makoto Kamada, Factorization of 77...77477...77, updated Dec 11 2018.
Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).
FORMULA
a(n) = 7*A138148(n) + 4*10^n.
G.f.: (4 + 303*x - 1000*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.
E.g.f.: (1/9)*exp(x)*(70*exp(99*x) - 27*exp(9*x) - 7). - Stefano Spezia, Feb 08 2020
MAPLE
A332174 := n -> 7*(10^(n*2+1)-1)/9 - 3*10^n;
MATHEMATICA
Array[7 (10^(2 # + 1) - 1)/9 - 3*10^# &, 15, 0]
PROG
CROSSREFS
Cf. A138148 (cyclops numbers with binary digits only).
KEYWORD
nonn,base,easy
AUTHOR
M. F. Hasler, Feb 08 2020
STATUS
approved