OFFSET
0,2
LINKS
Chai Wah Wu, Table of n, a(n) for n = 0..10000
Index entries for linear recurrences with constant coefficients, signature (1,4,-4,-6,6,4,-4,-1,1).
FORMULA
a(n) = #{i:A057135(i)<10^n}.
For n > 0, a(n) = Sum_{i=1..n} A218035(i).
a(n) = a(n-1) + 4*a(n-2) - 4*a(n-3) - 6*a(n-4) + 6*a(n-5) + 4*a(n-6) - 4*a(n-7) - a(n-8) + a(n-9) for n > 9.
G.f.: (-x^9 + x^7 - x^6 - 6*x^5 - x^4 + 7*x^3 + 2*x^2 - 3*x - 1)/((x - 1)^5*(x + 1)^4).
a(n) = 1491 + 904*n + 510*n^2 - 52*n^3 + 6*n^4 + (-1)^n * (45 - 296*n + 42*n^2 - 4*n^3) for n>0. - Greg Dresden, Jun 20 2021
EXAMPLE
a(2) = 6 since the only palindromes < 100 whose square are palindromes are 0,1,2,3,11,22.
PROG
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Chai Wah Wu, Apr 04 2021
STATUS
approved