URL: https://oeis.org/A359143/a359143.py.txt
# Python program for an iteration defined by Eric Angelini [now OEIS A359143]
# by Michael S. Branicky [written Jul 26 2022]
# [to convert strings to numbers in A359143, use: an = int(s) if s[0] != "0" else -int(s)]
# SOURCE:
# Eric Angelini, Add and erase: does the iteration end?, math-fun mailing list, Jul 26 2022
def iterate(s, printevery=10**6):
i, seen, longest = 0, {s}, s
while True:
i += 1
addon = str(sum(map(int, s)))
s += addon
if s[0] in addon:
s = s.replace(s[0], "")
if len(s) > len(longest):
longest = s
if len(s) == 0:
print(f"empty string ('{s}') reached at step {i}")
print(f"longest string encountered: {longest} (length {len(longest)})")
break
if s in seen:
print(f"cycle reached at step {i}, string '{s}'")
print(f"longest string encountered: {longest} (length {len(longest)})")
break
seen.add(s)
if i%printevery == 0:
print(f"iteration {i}: {s} (length {len(s)})")
iterate("11", printevery=10**5)
