A015977 Two iterations of Reverse and Add are needed to reach a palindrome.

5, 6, 7, 8, 9, 19, 28, 37, 39, 46, 48, 49, 55, 57, 58, 64, 66, 67, 73, 75, 76, 82, 84, 85, 91, 93, 94, 109, 119, 129, 139, 149, 150, 151, 152, 153, 154, 159, 160, 161, 162, 163, 169, 170, 171, 172, 173, 179, 189, 208, 218, 219, 228, 229, 238, 239, 248

Offset: 0

Author

Robert G. Wilson v

Keywords

• nonn
• base

Comments

The number of iterations starts at 1, so palindromes (cf. A002113) are not excluded. The corresponding sequence excluding palindromes is A065207.

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000
• Index entries for sequences related to Reverse and Add!

Crossrefs

Cf. A002113, A065207.

Programs

Mathematica

Select[Range[250],Boole[PalindromeQ/@Rest[NestList[#+IntegerReverse[#]&,#,2]]] == {0,1}&] (* Harvey P. Dale, May 11 2022 *)

Python

def ra(n): s = str(n); return int(s) + int(s[::-1])
def ispal(n): s = str(n); return s == s[::-1]
def aupto(limit):
  alst = []
  for k in range(limit+1):
    k2 = ra(k)
    if ispal(k2): continue
    if ispal(ra(k2)): alst.append(k)
  return alst
print(aupto(250)) # Michael S. Branicky, May 06 2021