OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,0,0,0,12,0,0,0,0,0,0,0,0,-21,0,0,0,0,0,0,0,0,10).
FORMULA
a(n) = d*A014824(m) where d = (n-1) mod 9 + 1 and m = ceiling(n/9). - Jon E. Schoenfield, Jul 22 2021
G.f.: x*(1 + 2*x + 3*x^2 + 4*x^3 + 5*x^4 + 6*x^5 + 7*x^6 + 8*x^7 + 9*x^8)/((1 - x^9)^2*(1 - 10*x^9)). - Stefano Spezia, Jul 26 2021
EXAMPLE
a(1) = 1,
a(2) = 2,
a(3) = 3,
...
a(9) = 9;
a(10) = 1 + 11 = 12,
a(11) = 2 + 22 = 24,
a(12) = 3 + 33 = 36,
...
a(18) = 9 + 99 = 108;
a(19) = 1 + 11 + 111 = 123,
a(20) = 2 + 22 + 222 = 246,
a(21) = 3 + 33 + 333 = 369,
...
a(27) = 9 + 99 + 999 = 1107; ...
MATHEMATICA
Table[m*(10^(1+k)-10-9*k)/81, {k, 6}, {m, 9}]//Flatten (* Stefano Spezia, Aug 17 2021 *)
PROG
CROSSREFS
KEYWORD
nonn,base,easy,changed
AUTHOR
Jwalin Bhatt, Jul 22 2021
STATUS
approved