21061

Properties

Appears in sequences

• a(n) is the solution to the postage stamp problem with 4 denominations and n stamps.at n=34A001209
• a(n)=2a(n-1)+3a(n-2)+2a(n-3)+3a(n-4).at n=8A022015
• a(n) = sum of cubes of p(j) - p(i), for 0 <= i < j <= n, where p(0) = 1.at n=6A024527
• Primes p such that x^27 = 2 has no solution mod p, but x^9 = 2 has a solution mod p.at n=6A059354
• a(2n) = concatenation of 4n+1 and 4n+2, a(2n+1) = concatenation of the two most nearly equal numbers whose product is a(2n).at n=11A068517
• Primes p such that x^9 = 2 has a solution mod p, but x^(9^2) = 2 has no solution mod p.at n=7A070185
• Record-setting differences between adjacent elements of the Mian-Chowla sequence A005282.at n=38A080222
• Numbers k such that k, sigma(k) and phi(k) have the same decimal digits (ignoring multiplicity).at n=30A082059
• Twin primes associated with A087900.at n=9A087901
• Numbers k such that 4*10^k+3 is prime.at n=18A101397
• Prime numbers p such that p +- ((p-1)/6) are primes.at n=22A137724
• Primes congruent to 16 mod 61.at n=38A142814
• Sums of the form (twin primes + 1) which are also an upper twin prime.at n=10A158870
• Primes obtained from other primes by pre-concatenating with 2.at n=39A165243
• List of 4-tuples of twin primes q, p, p+2 and q+2 such that 2*q<p<p+2<2*(q+2).at n=42A176821
• The least number s having exactly n fours in the continued fraction of sqrt(s).at n=26A206584
• Numerator of Sum_{k=1..n}(-1)^k/phi(k), where phi = A000010.at n=38A211177
• Primes p=u^2+v^2 such that p+u or p+v is the next prime after p.at n=25A213996
• Primes p for which exactly five bases b with 1 < b < p exist such that p is a base b Wieferich prime.at n=8A255208
• Primitive prime factors of the cyclotomic polynomial sequence Phi(9,k) in the order in which they occur.at n=16A256144