203 = 113 + 123 +133 + 143
220 - 1 = 3 * 5 * 5 * 11 * 31 * 41
20 = 12 + 3 − 45 + 67 − 8 − 9
20 = 98 + 7 − 65 + 4 − 3 − 21
20 = 0^5 − 1^9 − 2^7 − 3^8 + 4^6 + 5^3 + 6^1 + 7^4 + 8^0 + 9^2
20 = 2^2 + 4^2
20 = (1 + 1) × (11 − 1)
= 22 − 2
= 3 × 3 + 33/3
= 4 + 4 × 4 = 4 ×(4 ÷ 4 + 4) = (44 − 4) ÷ √4
= 5 × 5 − 5
= 6 + 6 + 6 + (6 + 6)/6
= 7 + 7 + 7 − 7/7
= 8 + (88 + 8)/8
= 9 + 99/9
1020 - 1 = 3 * 3 * 11 * 41 * 101 * 271 * 3541 * 9091 * 27961
a(n) = 2^n + n, n = 4
20 = binomial(4 + 2, 3) is the 4th tetrahedral number.
Abundant number : 12, 18, 20, 24, 30, 36, 40, 42, 48, 54, 56, 60, 66, 70, 72, 78, 80, 84, 88, 90, 96, 100, 102, 104, 108, 112, 114, 120, ... (sequence A005101 in the OEIS).
Moser-de Bruijn sequence: sums of distinct powers of 4
Numbers k such that k^4 + 1 is prime.
Number k such that (11*10^k + 19)/3 is prime
Number k such that (16*10^k - 31)/3 is prime.
Numbers k such that k^2 divides 9^k - 1 (12157665459056928800)
Number of Integer partitions of 20: 627
Numbers of edges of regular polygon constructible with unmarked straightedge and compass.
The ring of integers of the field Q(sqrt(-20)) has class number 2.
Representations, Binary to Hexadecimal:
10100_2
202_3
110_4
40_5
32_6
26_7
24_8
22_9
19_11
18_12
17_13
16_14
15_15
14_16
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