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Talk:Truncatable primes: Difference between revisions
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→redefinition of truncatable primes: dear, cheap, rare, hateful numbers, and then some. -- ~~~~
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:::Hi Gerard, I still can't see how talking about taking a digit would mean anything but a decimal digit from a base-10 representation of a prime? The task description on RC leaves out any mention of numerical bases. You introduce bases above when you talk of the number of right-truncatable primes but if you had just said that "There are only 83 right-truncatable primes" then wouldn't a base of 10 be automatically inferred? --[[User:Paddy3118|Paddy3118]] 21:48, 12 September 2012 (UTC)
:::: No, as others have discussed this (outside of Rosetta Code) and are careful in mentioning what base is being meant. The number, 787 in octal is 1423. If you take the digit '''4''' (from the 1423 number) ... this statement doesn't infer that 1423 is base ten. There are a few number sequences that are in (or implied) base ten (but some sequences could be in other bases):
* look-and-say (look, then say how many digits there are, in order, of a positive integer)
* apocalypse primes (a prime that is exactly 666 digits)
* apocalyptic (a positive integer power of two that contain a '''666''' in the number)
* Armstrong (N-digit non-negative integers which are equal to their sum of the Nth powers of their digits)
* dear (integers whose digits are 7, 8, or 9, but not two of any of those)
* dearer (integers whose digits are any of two digits of 7, 8, or 9)
* dearest (integers which have at least one each of the digits 7, 8, or 9)
* cheap/cheaper/cheapest (similar to above, for digits 1, 2, or 3)
* middling/middlinger/middlingest (similar to above, for digits 4, 5, or 6)
* curvaceous (non-negative integers whose digits are written with curves (digits 3, 6, 8, 9, and 0)
* curviliner (positive integers whose digits are written with curves and straight lines (digits 2 or 5)
* deBruijn (a sequences of digits for non-negative integer N such that every possible combination of digits is in the sequence)
* digCount, digitCount (the number of each of the digits in a non-negative integer)
* digitSequence (number of unique numbers that can be found in the base ten expression of the non-negative integer N)
* hateful (positive integers which contain the numerals '''666''')
* prime digit primes (which all digits of P are also prime)
* rare (positive integers in which N+r and N-r are equal, and N is non-palindromic, r is the reverse of N)
* rep unit primes (primes which only contain the digit one)
(Pardon me if some of those sequences should be capitalized.) Also pardon me if I didn't get the exact definition stated correctly, I was trying to be succinct so that the definition would fit on one line. I was switching between digits and numerals, numbers and integers, and whatnot.
<br>A few sequences are shown in base ten, but use another base, such as xenodrome numbers (base 12), xenodrome numbers are integers, which expressed in base 12, has every numeral (digit) different from each other, that is, each digit is unique). -- [[User:Gerard Schildberger|Gerard Schildberger]] 22:46, 12 September 2012 (UTC)
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