OFFSET
1,1
COMMENTS
Number of terms of A061230 which are n digits long.
LINKS
EXAMPLE
a(1) = 3 because there are 3 single-digit numbers: 0, 2, 8 such that b + b = m^2, for example, 8 + 8 = 16 = 4^2;
a(2) = 8 because there are 8 two-digit numbers: 29, 38, 47, 56, 65, 74, 83, 92 such that bc + cb = m^2, for example, 29 + 92 = 121 = 11^2.
MATHEMATICA
a[n_]:=Length[Select[Table[k, {k, 10^(n-1), 10^n-1}], IntegerQ[Sqrt[#+FromDigits[Reverse[IntegerDigits[#]]]]]&]]; Array[a, 10] (* Stefano Spezia, Dec 09 2022 *)
PROG
(Python)
from math import isqrt
def s(n): return isqrt(n)**2 == n
def c(n): return s(n + int(str(n)[::-1]))
def a(n): return 3 if n == 1 else sum(1 for k in range(10**(n-1), 10**n) if c(k))
print([a(n) for n in range(1, 7)]) # Michael S. Branicky, Dec 08 2022
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Nicolay Avilov, Dec 08 2022
EXTENSIONS
a(9)-a(10) from Michael S. Branicky, Dec 08 2022
a(11)-a(20) from Talmon Silver, Dec 25 2022
STATUS
approved