[seqfan] Concatenation

Charles Greathouse charles.greathouse at case.edu
Fri Apr 23 17:40:06 CEST 2010

How should concatenation be represented in the OEIS?

Giovanni Resta uses // for concatenation, as in A115429.
Leroy Quet uses U for concatenation, as in A165784.
Farideh Firoozbakht uses . for concatenation, as in A115437.
Patrick De Geest uses 'foo followed by bar' (with the quotes), as in
A034821; but see also A032711.
Amarnath Murthy denotes concatenation by concatenation, as in A089710.

Of course there's no reason that we need to have a symbolic form, but
these examples show that the need for some symbolic representation has
come up many times.  I have no strong preference except to
standardize, whether on a particular form (these or a novel one) or to
use no such representation.

There's not much guidance from the popular programs, which use verbose forms:
Pari uses eval(Str(a1, ..., an)).  Mathematica uses
FromDigits[Join[IntegerDigits[a1], ..., IntegerDigits[an]]] or
ToExpression[StringJoin[ToString[a1], ..., ToString[an]]]. It looks
like Maple must use (and the others could use) multiplication by an
appropriate power of 10 and addition.

Charles Greathouse
Case Western Reserve University

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