[seqfan] Re: Can this sequence be defined well: 7, 16, 34, ... ?

hv at crypt.org hv at crypt.org
Wed Apr 29 00:50:08 CEST 2020

Alonso Del Arte <alonso.delarte at gmail.com> wrote:
:According to the documentation for java.math.MathContext <
:https://docs.oracle.com/javase/7/docs/api/java/math/MathContext.html>, the
:confusingly named DECIMAL32 is good for 32 bits of precision, or 7 decimal
:digits; DECIMAL64 is good for 64 bits or 16 digits; and DECIMAL128 is good
:for 128 bits or 34 digits. I've verified in the Scala REPL that there's no
:DECIMAL256. But if there was, what would be its decimal digit precision?
:I thought maybe if I searched the OEIS for "7, 16, 34" I might find the
:answer. The set of search results is small, though just big enough for me
:to think that maybe I've overlooked the answer. Which would mean only one
:of the results has the answer.
:But perhaps that also assumes the sequence can be defined well and it's
:already in the OEIS. Can it be well-defined? If so, is it already in the
:OEIS? It it isn't, does it need to be?

This appears to be IEEE-754, in which only DECIMAL64 and DECIMAL128 are
defined as basic formats; however any multiple of 32 bits is defined
as an interchange format.

https://en.wikipedia.org/wiki/Binary_integer_decimal gives some details
of one of the two ways that the numbers may be represented (the other
being https://en.wikipedia.org/wiki/Densely_packed_decimal); I think it
should be possible from the details there to work out the range of the
interchange formats for other bit numbers including 256.


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