121
domain: N
Properties
Digital Properties
- Digit Count
- 3
- Digit Sum
- 4
- Digital Root
- 4
- Palindromic Number
- yes
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 3
- Divisor Sum
- 133
- Proper Divisor Sum (Aliquot Sum)
- 12
- 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
- 110
- Möbius Function
- 0
- Radical
- 11
- Omega Function (Ω)
- 2
- Little Omega Function (ω)
- 1
Special
- Factorial
- no
- Catalan Number
- no
- Bell Number
- no
- Motzkin Number
- no
- Primorial
- no
Figurate Numbers
- Fibonacci Number
- no
- Triangular Number
- no
- Perfect Square
- yes
- 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
- 95
- Smith Number
- yes
Primality
- Prime
- no
- Composite Number
- yes
- Semiprime
- yes
- Squarefree Number
- no
- Prime Power
- yes
- Prime Factorization
- no
- Twin Prime
- no
- Mersenne Prime
- no
- Sophie Germain Prime
- no
- Safe Prime
- no
- Powerful Number
- yes
- Achilles Number
- no
- Perfect Power
- yes
- Smooth Number
- no
- Carmichael Number
- no
Classification
- Even
- no
- Odd
- yes
Names
- German
- einshunderteinundzwanzig· ordinal: einshunderteinundzwanzigste
- English
- one hundred twenty-one· ordinal: one hundred twenty-first
- Spanish
- ciento veintiuno· ordinal: 121º
- French
- cent vingt et un· ordinal: cent vingt et unième
- Italian
- centoventuno· ordinal: 121º
- Latin
- centum viginti unus· ordinal: 121.
- Portuguese
- cento e vinte e um· ordinal: 121º
Appears in sequences
- 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=57A000028
- Numbers k such that (2k)^4 + 1 is prime.at n=34A000059
- Odious numbers: numbers with an odd number of 1's in their binary expansion.at n=60A000069
- Number of trees of diameter 4.at n=14A000094
- Central polygonal numbers (the Lazy Caterer's sequence): n(n+1)/2 + 1; or, maximal number of pieces formed when slicing a pancake with n cuts.at n=15A000124
- 3*n - 2*floor(sqrt(4*n+5)) + 5.at n=48A000277
- a(n) = 2^n - n.at n=7A000325
- Primes and squares of primes.at n=34A000430
- n written in base where place values are positive cubes.at n=44A000433
- n followed by n^2.at n=21A000463
- Squares that are not the sum of 2 nonzero squares.at n=8A000548
- Number of nonnegative solutions of x^2 + y^2 = z in first n shells.at n=57A000592
- Numbers k such that (1,k) is "good".at n=5A000696
- Expansion of Product_{k >= 1} (1 - x^k)^6.at n=30A000729
- Numbers beginning with a vowel in English.at n=35A000852
- Numbers ending with a vowel in American English.at n=53A000861
- Numbers beginning with letter 'o' in English.at n=22A000865
- "First factor" (or relative class number) h- for cyclotomic field Q( exp(2 Pi / prime(n)) ).at n=12A000927
- Powers of primes. Alternatively, 1 and the prime powers (p^k, p prime, k >= 1).at n=41A000961
- Powers of 11: a(n) = 11^n.at n=2A001020