The OEIS meta sequence and subway stations

3 days ago

A051070 is a sequence where a(n) is the n-th term of OEIS sequence A_n, or -1 if A_n lacks enough terms.
The sequence starts with values like 1, 2, 1, 0, and includes very large entries, such as a(58) with 58669977298272603 digits.
Some terms, like a(66), are unknown due to limitations in known values of underlying sequences.
The first occurrence of a(n) = -1 is at n=53 and 54, because New York subway line sequences lack enough stops.
OEIS includes sequences based on real-world data, such as subway stops, challenging the notion of purely mathematical definitions.
A102288 is a related sequence defined as 1 + the n-th term of A_n, leading to self-referential paradoxes.
A debate exists in the OEIS comments between whimsy and well-definedness, with Neil Sloane favoring paradoxical definitions.

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