66
domain: N
Properties
Digital Properties
- Digit Count
- 2
- Digit Sum
- 12
- Digital Root
- 3
- Palindromic Number
- yes
- Repdigit
- yes
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 3
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 144
- Proper Divisor Sum (Aliquot Sum)
- 78
- Abundant Number
- yes
- Perfect Number
- no
- Deficient Number
- no
- Highly Composite
- no
- Weird Number
- no
- Untouchable Number
- no
- Primitive Abundant
- yes
Derived Values
- Euler's Totient
- 20
- Möbius Function
- -1
- Radical
- 66
- Omega Function (Ω)
- 3
- Little Omega Function (ω)
- 3
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- yes
- Perfect Square
- no
- Perfect Cube
- no
- Pentagonal Number
- no
- Hexagonal Number
- yes
- 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
- 27
- Smith Number
- no
Classification
- Natural
- yes
- Even
- yes
- Odd
- no
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- no
- 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
Names
- German
- sechsundsechzig· ordinal: sechsundsechzigste
- English
- sixty-six· ordinal: sixty-sixth
- Spanish
- sesenta y seis· ordinal: 66º
- French
- soixante-six· ordinal: soixante-sixième
- Italian
- sessantasei· ordinal: 66º
- Latin
- sexaginta sex· ordinal: 66.
- Portuguese
- sessenta e seis· ordinal: 66º
Appears in sequences
- Euler totient function phi(n): count numbers <= n and prime to n.at n=66A000010
- Mosaic numbers or multiplicative projection of n: if n = Product (p_j^k_j) then a(n) = Product (p_j * k_j).at n=65A000026
- The positive integers. Also called the natural numbers, the whole numbers or the counting numbers, but these terms are ambiguous.at n=65A000027
- Let k = p_1^e_1 p_2^e_2 p_3^e_3 ... be the prime factorization of n. Sequence gives k such that the sum of the numbers of 1's in the binary expansions of e_1, e_2, e_3, ... is odd.at n=30A000028
- Numbers that are not squares (or, the nonsquares).at n=57A000037
- Local stops on New York City 1 Train (Broadway-7 Avenue Local) subway.at n=8A000053
- Numbers k such that (2k)^4 + 1 is prime.at n=19A000059
- A Beatty sequence: a(n) = floor(n/(e-2)).at n=47A000062
- Number of series-parallel networks with n unlabeled edges. Also called yoke-chains by Cayley and MacMahon.at n=5A000084
- Number of dissections of an n-gon, rooted at an exterior edge, asymmetric with respect to that edge.at n=6A000150
- Lower Wythoff sequence (a Beatty sequence): a(n) = floor(n*phi), where phi = (1+sqrt(5))/2 = A001622.at n=40A000201
- a(8i+j) = 13i + a(j), where 1<=j<=8.at n=40A000202
- 3*n - 2*floor(sqrt(4*n+5)) + 5.at n=27A000277
- Number of rooted polyhedral graphs with n edges.at n=5A000287
- Number of trees of diameter 8.at n=3A000306
- Sums of three squares: numbers of the form x^2 + y^2 + z^2.at n=56A000378
- Hexagonal numbers: a(n) = n*(2*n-1).at n=6A000384
- Numbers of form x^2 + y^2 + 2*z^2.at n=61A000401
- Numbers that are the sum of three nonzero squares.at n=39A000408
- Numbers that are the sum of 4 nonzero squares.at n=50A000414