Properties of the Number 1981

One Thousand Nine Hundred Eighty-One

Basics

Value: 1980 → 1981 → 1982

Parity: odd

Prime: No

Previous Prime: 1979

Next Prime: 1987

Digit Sum: 19

Digital Root: 1

Palindrome: No

Factorization: 7 × 283

Divisors: 1, 7, 283, 1981

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 11110111101

Octal: 3675

Duodecimal: 1191

Hexadecimal: 7bd

Square: 3924361

Square Root: 44.50842616853577

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Central polygonal numbers: a(n) = n² - n + 1. A2061

a(n) is the smallest m > 1 such that m divides ∑_k=1..m prime(k)ⁿ. A85450

G.f.: ∏_k>=1 (1 + x^{2·k - 1}) / (1 - x^2·k). A6950

a(n) = 4·n² - 6·n + 3. A54569

Triangle read by rows of partial sums of binomial coefficients: T(n,k) = ∑_i=0..k binomial(n,i) (0 <= k <= n); also dimensions of Reed-Muller codes. A8949

Total number of ON states after n generations of cellular automaton based on hexagons. A151723

a(n) = 2ⁿ - 1 - n*(n+1)/2. A2662

a(n) = (n+1)*(n² +8·n +6)/6. Number of n-dimensional partitions of 4. Number of terms in 4th derivative of a function composed with itself n times. A8778

Numbers k such that k, k+1 and k+2 are products of two primes. A56809

Generalized 21-gonal (or icosihenagonal) numbers: m*(19·m - 17)/2 with m = 0, +1, -1, +2, -2, +3, -3, ... A303298