21757

Properties

Appears in sequences

• Primes of form k^2 + k + 1.at n=42A002383
• Primes that remain prime through 3 iterations of function f(x) = 2x + 3.at n=33A023273
• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 13.at n=16A031601
• Primes p such that x^49 = 2 has no solution mod p, but x^7 = 2 has a solution mod p.at n=8A059667
• Primes of the form 4*k^2 - 10*k + 7 with k positive.at n=25A073337
• Values of k such that the total number of 1's in the binary expansions of the first k integers is a multiple of k.at n=24A095376
• Primes for which the weight as defined in A117078 is 11 and the gap as defined in A001223 is 10.at n=26A119596
• Intersection of A061068 and A064270.at n=35A128996
• Triangle of the numerators of coefficients c(n,k) = [x^k] P(n,x) of some polynomials P(n,x).at n=31A141904
• Numerators of triangle T(n,k), n>=1, 0<=k<=n - 1, read by rows: T(n,k) is the coefficient of x^k in polynomial p_n for the n-th row sequence of A145153.at n=70A145140
• Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, 0), (-1, 1, 0), (0, 0, -1), (1, -1, 0), (1, 1, 1)}.at n=8A149677
• Primes p such that the multiplicative order of 2 modulo p is (p-1)/7.at n=24A152307
• Primes p of the form : p+p^2+p^3-+8=prime.at n=21A154823
• Largest element of a set of n primes with the property that the pairwise averages are all distinct primes, having the smallest largest element (A115631).at n=9A155463
• Number of nodes (or order) of a graph model obtained using an automata scheme on sets of order prime(n) >= 5 and in which all not halt states are linked by arcs (edges).at n=32A160772
• Primes of the form n^2 + n + 1 where n is nonprime.at n=32A185632
• Primes p congruent to 1 mod 12 such that (p + 1)/2 does not divide the numerator of the Bernoulli number B(p + 1).at n=23A232039
• Primes p such that p+2^4, p+2^6 and p+2^8 are all primes.at n=28A269257
• Primes p = x^2 + y^2 such that x - y is a cube greater than one.at n=27A282405
• a(n) is the least number such that d(a(n)) = d(R(a(n)))/n, where R(n) is the digit reverse of n and d(n) is the number of divisors of n.at n=20A284495