A347401 Lexicographically earliest sequence of distinct terms > 0 such that the sum n + a(n) forms a palindrome in base 10.

1, 2, 3, 4, 6, 5, 15, 14, 13, 12, 11, 10, 9, 8, 7, 17, 16, 26, 25, 24, 23, 22, 21, 20, 19, 18, 28, 27, 37, 36, 35, 34, 33, 32, 31, 30, 29, 39, 38, 48, 47, 46, 45, 44, 43, 42, 41, 40, 50, 49, 60, 59, 58, 57, 56, 55, 54, 53, 52, 51, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 80, 79, 78, 77, 76, 75, 74, 73

Offset: 1

Author

Eric Angelini and Carole Dubois, Aug 30 2021

Keywords

• base
• nonn

Examples

			For n = 4 we have a(4) = 4 and 4 + 4 = 8 is a palindrome in base 10;
for n = 5 we have a(5) = 6 and 5 + 6 = 11 is a palindrome in base 10;
for n = 6 we have a(6) = 5 and 6 + 5 = 11 is a palindrome in base 10;
for n = 7 we have a(7) = 15 and 7 + 15 = 22 is a palindrome in base 10;
for n = 8 we have a(8) = 14 and 8 + 14 = 22 is a palindrome in base 10; etc.
		

Crossrefs

Cf. A347335, A347336, A347400, A347402.

Programs

Python

def ispal(n): s = str(n); return s == s[::-1]
def aupton(terms):
    alst, seen = [1], {1}
    for n in range(2, terms+1):
        an = 1
        while an in seen or not ispal(n + an): an += 1
        alst.append(an); seen.add(an)
    return alst
print(aupton(200)) # Michael S. Branicky, Aug 30 2021