15 lines
349 B
Python
15 lines
349 B
Python
>>> from functools import lru_cache
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>>> @lru_cache(maxsize=1024)
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def ids(n):
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if n in {1, 89}: return n
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else: return ids(sum(int(d) ** 2 for d in str(n)))
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>>> ids(15)
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89
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>>> [ids(x) for x in range(1, 21)]
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[1, 89, 89, 89, 89, 89, 1, 89, 89, 1, 89, 89, 1, 89, 89, 89, 89, 89, 1, 89]
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>>> sum(ids(x) == 89 for x in range(1, 100000000))
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85744333
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>>>
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