21221

Properties

Appears in sequences

• Numbers that are the sum of 11 positive 8th powers.at n=39A003389
• Numbers that are the sum of 6 positive 9th powers.at n=10A003395
• a(n) is the concatenation of a(n-1) and a(n-2) with a(1)=1, a(2)=2.at n=4A008351
• Primes that contain digits 1 and 2 only.at n=8A020450
• Primes that remain prime through 2 iterations of function f(x) = 8x + 1.at n=37A023260
• n written in fractional base 3/2.at n=22A024629
• Primes having only {0, 1, 2} as digits.at n=23A036953
• Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,2.at n=4A037575
• Number of primes less than 10000n.at n=23A038813
• k th digit of a(n) = number of different digits within 2 places of k (not including k).at n=13A039987
• Primes p from A031924 such that A052180(primepi(p)) = 19.at n=17A052235
• McKay-Thompson series of class 39B for Monster.at n=50A058660
• Numbers whose product of decimal digits equals its sum of binary digits.at n=30A064003
• Primes p such that (x1*x2*...*xk)^(x1+x2+...+xk) = (x1+x2+...+xk)^(x1*x2*...*xk) where x1x2...xk are the digits of p in base 10.at n=11A064157
• Prime numbers such that sum of digits equals product of digits.at n=10A066306
• Primes p equal to the sum of two successive sexy primes + 1 such that p + 6 is also prime.at n=30A104043
• Primes with maximal digit = 2.at n=20A106100
• Primes with digital product = 8.at n=11A107694
• Primes in which the frequency of every digit is also prime.at n=18A113615
• Ternary emirpimes.at n=19A119684