221
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 5
- Digital Root
- 5
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 4
- Divisor Sum
- 252
- Proper Divisor Sum (Aliquot Sum)
- 31
- Abundant Number
- no
- Perfect Number
- no
- Deficient Number
- yes
- Highly Composite
- no
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- no
Derived Values
- Euler's Totient
- 192
- Möbius Function
- 1
- Radical
- 221
- Omega Function (Ω)
- 2
- Little Omega Function (ω)
- 2
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- no
- Perfect Square
- no
- Perfect Cube
- no
- Pentagonal Number
- no
- Hexagonal Number
- no
- Lucas Number
- no
- Tetrahedral Number
- no
- Pell Number
- no
- Tribonacci Number
- no
- Pronic Number
- no
Recreational
- Happy Number
- no
- Harshad Number
- no
- Narcissistic Number
- no
- Collatz Steps
- 114
- Smith Number
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- Squarefree Number
- yes
- Prime Power
- no
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- no
- Achilles Number
- no
- Perfect Power
- no
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- zweihunderteinundzwanzig· ordinal: zweihunderteinundzwanzigste
- English
- two hundred twenty-one· ordinal: two hundred twenty-first
- Spanish
- doscientos veintiuno· ordinal: 221º
- French
- deux cent vingt et un· ordinal: deux cent vingt et unième
- Italian
- duecentoventuno· ordinal: 221º
- Latin
- ducenti viginti unus· ordinal: 221.
- Portuguese
- duzentos e vinte e um· ordinal: 221º
Appears in sequences
- Number of positive integers <= 2^n of form x^2 + 10 y^2.at n=10A000024
- Numbers k such that (2k)^4 + 1 is prime.at n=54A000059
- Let A(n) = #{(i,j,k): i^2 + j^2 + k^2 <= n}, V(n) = (4/3)Pi*n^(3/2), P(n) = A(n) - V(n); A000092 gives values of n where |P(n)| sets a new record; sequence gives (nearest integer to, I believe) P(A000092(n)).at n=16A000223
- Topswops (1): start by shuffling n cards labeled 1..n. If top card is m, reverse order of top m cards, then repeat. a(n) is the maximal number of steps before top card is 1.at n=18A000375
- Number of partitions of n into parts of 3 kinds.at n=6A000716
- Genus of complete graph on n nodes.at n=54A000933
- a(n) = ceiling(n^2/2).at n=21A000982
- Numbers of form m*k with m+1 <= k <= 2m-1.at n=62A001284
- Number of partitions of n into at most 5 parts.at n=21A001401
- Number of graphs with n nodes and n edges.at n=8A001434
- a(n) = (6*n+1)*(6*n+5).at n=2A001513
- a(n) = n^2 written in base 3.at n=5A001738
- Centered square numbers: a(n) = 2*n*(n+1)+1. Sums of two consecutive squares. Also, consider all Pythagorean triples (X, Y, Z=Y+1) ordered by increasing Z; then sequence gives Z values.at n=10A001844
- Apply partial sum operator twice to Fibonacci numbers.at n=9A001924
- v-pile positions of the 4-Wythoff game with i=1.at n=42A001964
- Nearest integer to n^2/8.at n=42A001971
- Numbers dividing A002037(i) and larger than A002037(i-1), for some i>0.at n=15A002038
- Numbers y such that p^2 = x^2 + y^2, 0 < x < y, p = A002144(n).at n=21A002365
- Numbers of the form (p^2 - 49)/120 where p is prime.at n=18A002382
- Odd squarefree numbers with an even number of prime factors that have no prime factors greater than 31.at n=28A002557