21001

Properties

Appears in sequences

• "DHK[ 7 ]" (bracelet, identity, unlabeled, 7 parts) transform of 1,1,1,1,...at n=18A032248
• Primes having only {0, 1, 2} as digits.at n=18A036953
• Lexicographically earliest strictly increasing base 3 autovarious sequence: a(n) = number of distinct a(k) mod 3^n (written in base 3).at n=25A037091
• Number of ways of placing n nonattacking (normal) queens on n X n board, solutions similar on the torus count only once.at n=13A062165
• Primes whose sum of digits is 4.at n=11A062339
• a(1) = 2; a(n+1) is the smallest prime > a(n) which differs from it in every digit.at n=32A068853
• Largest n-digit prime with minimum digit sum.at n=4A069664
• Numbers k such that k, sigma(k) and phi(k) have the same decimal digits (ignoring multiplicity).at n=27A082059
• Prime numbers such that first reversing digits and after squaring equals the result of first-squaring and after-reversing. Primes in A085305.at n=32A085306
• Primes of the form (prime(k-1)+1)*(prime(k+1)-1) + 1, k>1.at n=11A087106
• Primes with maximal digit = 2.at n=15A106100
• Greater of number pair whose squares are reversals of each other, with no leading zeros allowed.at n=30A106324
• a(n) = the first prime in the earliest sequence of 2n+1 consecutive primes whose average is prime.at n=42A108231
• a(n) = 49n^2 - 28n - 20.at n=20A118058
• Prime values of integers written in factorial base, interpreted as in base 10.at n=41A121402
• Floor(n*exp(sec(n))).at n=13A134899
• Primes congruent to 17 mod 61.at n=37A142815
• Primes where the first digit equals the sum of all the other digits.at n=25A156307
• Primes of the form 1000*k + 1.at n=7A156655
• Primes sorted on digit sums, then on the primes.at n=15A157715