206 (number)

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← 205 206 207 →
Cardinal two hundred six
Ordinal 206th
(two hundred sixth)
Factorization 2 × 103
Divisors 1, 2, 103, 206
Greek numeral ΣϚ´
Roman numeral CCVI, ccvi
Binary 110011102
Ternary 211223
Senary 5426
Octal 3168
Duodecimal 15212
Hexadecimal CE16

206 (two hundred [and] six) is the natural number following 205 and preceding 207.

In mathematics

206 is both a nontotient and a noncototient. [1] 206 is an untouchable number. [2] It is the lowest positive integer (when written in English as "two hundred and six") to employ all of the vowels once only, not including Y. The other numbers sharing this property are 230, 250, 260, 602, 640, 5000, 8000, 9000, 26,000, 80,000 and 90,000. [3] 206 and 207 form the second pair of consecutive numbers (after 14 and 15) whose sums of divisors are equal. [4] There are exactly 206 different linear forests on five labeled nodes, [5] and exactly 206 regular semigroups of order four up to isomorphism and anti-isomorphism. [6]

References

  1. ↑ Sloane, N. J. A. (ed.). "SequenceA058763(Integers which are neither totient nor cototient)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  2. ↑ "Sloane's A005114 : Untouchable numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. 2016-04-18. Retrieved 2016-04-18.
  3. ↑ Sloane, N. J. A. (ed.). "SequenceA058180(Numbers whose English names include all five vowels exactly once)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  4. ↑ Sloane, N. J. A. (ed.). "SequenceA002961(Numbers n such that n and n+1 have same sum of divisors)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  5. ↑ Sloane, N. J. A. (ed.). "SequenceA011800(Number of labeled forests of n nodes each component of which is a path)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.
  6. ↑ Sloane, N. J. A. (ed.). "SequenceA001427(Number of regular semigroups of order n, considered to be equivalent when they are isomorphic or anti-isomorphic (by reversal of the operator))". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation.


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