[seqfan] Re: My first base-10 related question here, I think

franktaw at netscape.net franktaw at netscape.net
Fri Jun 26 21:45:33 CEST 2009

Yes.  Any time a sequence is pulling numbers out of a sequence of 
digits that includes zeros, there should be a comment (or part of the 
definition) specifying what is being done with zeros.

There are two main choices: allow terms to start with zero (as here), 
or don't permit a digit preceding a zero to mark the end of an 
extracted number.  There are examples in the database doing it both 

Incidentally, it would be good to have a cross-reference from A074721 
to A069090.  Does every member of A069090 occur in A074721?

(I am sending in more terms and a b-file for A069090.)

Franklin T. Adams-Watters

-----Original Message-----
From: Hans Havermann <pxp at rogers.com>

I just want to bring up something that is not necessarily a problem
for this sequence but I'd like someone's opinion on it regardless.
When the primes 691, 701, 709, and 719 get concatenated and digitized,
we end up with: {..., 6, 9, 1, 7, 0, 1, 7, 0, 9, 7, 1, 9, ...}. These
will end up in A074721 as terms #98 - #102: {691, 7, 17, 97, 19}.
Terms #100 & #101 have associated with them *unstated* leading zeros.
This makes it difficult to construct the concatenated primes from just
the sequence terms. Perhaps a comment to that effect might alert the
unwary. The alternative would be to complicate the definition of the
sequence to exclude leading zeros from existing, not the best solution.

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