1990
domain: N
Properties
Digital Properties
- Digit Count
- 4
- Digit Sum
- 19
- Digital Root
- 1
- Palindromic Number
- no
- Repdigit
- no
- Automorphic
- no
- Kaprekar Number
- no
- Multiplicative Persistence
- 1
Divisibility
- Divisor Count
- 8
- Divisor Sum
- 3600
- Proper Divisor Sum (Aliquot Sum)
- 1610
- 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
- 792
- Möbius Function
- -1
- Radical
- 1990
- 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
- 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
- 24
- Smith Number
- no
- Vampire Number
- 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
Classification
- Even
- yes
- Odd
- no
Appears in sequences
- a(n) = floor(n*phi^11), where phi is the golden ratio, A001622.at n=10A004926
- a(n) = round(n*phi^11), where phi is the golden ratio, A001622.at n=10A004946
- Stella octangula numbers: a(n) = n*(2*n^2 - 1).at n=10A007588
- Number of lattice points inside circle of radius n is 4(a(n)+n)-3.at n=50A007882
- Coordination sequence T1 for Zeolite Code ATT.at n=32A008041
- Coordination sequence T2 for Zeolite Code NON.at n=27A008213
- sec(arcsinh(x)+arctan(x))=1+4/2!*x^2+56/4!*x^4+1990/6!*x^6...at n=3A013113
- Numbers n such that phi(n + 1) | sigma(n) for n congruent to 1 (mod 3).at n=14A015817
- Numbers k such that phi(k + 12) | sigma(k) for k not congruent to 0 (mod 3).at n=17A015850
- Coordination sequence T6 for Zeolite Code TER.at n=30A016438
- Numbers k such that the continued fraction for sqrt(k) has period 36.at n=18A020375
- Numbers k such that Fibonacci(k) == 55 (mod k).at n=31A023181
- a(n) = position of n^3 + (n+1)^3 + (n+2)^3 in A003072.at n=16A024972
- a(n) = s(1)s(n) + s(2)s(n-1) + ... + s(k)s(n-k+1), where k = [ n/2 ], s = A000201 (lower Wythoff sequence).at n=19A025118
- (d(n)-r(n))/5, where d = A006527 and r is the periodic sequence with fundamental period (4,1,4,0,1).at n=29A026036
- Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 18 ones.at n=30A031786
- Fractional part of square root of a(n) starts with 6: first term of runs.at n=42A034112
- a(n) = a(n-1) + prime(n-1), with a(1)=2.at n=33A036439
- Numbers n with property that, reading binary expansion of n from right to left, run lengths strictly increase.at n=44A037015
- Numbers k such that 0 and 9 occur juxtaposed in the base-10 representation of k but not of k-1.at n=38A043224