21149

Properties

Appears in sequences

• Prime number spiral (clockwise, West spoke).at n=24A054570
• First of triples of consecutive happy numbers, i.e., the first of three consecutive integers each of which is a happy number (A007770).at n=22A072494
• Primes and their indices such that when their respective SOD's are both prime, the SOD of the index is the nextprime of the prime SOD.at n=33A117458
• a(n) = 11 + floor(Sum_{j-1..n-1} a(j)/4).at n=34A120168
• Number of free hexagonal polygons of symmetry class D_(2h) and area n.at n=31A121211
• Primes p such that p*q-p-q and p*q+p+q are prime where q=nextprime(p).at n=37A128548
• Primes congruent to 43 mod 61.at n=37A142841
• Primes which are the sum of two numbers of the form k*(k+1)^2/2.at n=41A210646
• Numbers k such that replacing each digit d in the decimal expansion of k with d^3 yields a prime each time, when done recursively three times.at n=12A316982
• Number of compositions (ordered partitions) of n into distinct parts having a common factor > 1 with n.at n=50A332003
• Numbers b > 1 such that the smallest four primes, i.e., 2, 3, 5 and 7 are base-b Wieferich primes.at n=22A339533
• Numbers N such that N + the sum of the cubes of its digits is again a third power.at n=20A362953
• Primes p such that the sum of cubes of the 4 consecutive primes starting with p is twice a prime.at n=22A368637
• Prime numbersat n=2377