23005
domain: N
Appears in sequences
- Numbers k such that the Woodall number k*2^k - 1 is prime.at n=22A002234
- Triangular numbers with sum of digits = 10.at n=27A068129
- Triangular numbers whose digit permutations yield at least two further triangular numbers.at n=18A069674
- Triangular numbers with internal digits also forming a triangular number.at n=34A069702
- Triangular number x such that x + reverse of x is a prime.at n=9A072387
- Products of members of pairs in A075333.at n=37A075337
- Triangular numbers whose internal digits form a triangular number. Or triangular number such that deleting the MSD and LSD leaves a triangular number.at n=48A077366
- Triangular numbers whose sum of aliquot divisors is a prime number.at n=16A083676
- Values that show the slow decrease in the Andrica function Af(k) = sqrt(p(k+1)) - sqrt(p(k)), where p(k) denotes the k-th prime.at n=30A084977
- Numbers k such that 3*10^k + 8*R_k - 7 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=19A102978
- Triangular numbers congruent to 1 or 5 mod 6.at n=35A128880
- Numbers k such that k and k^2 use only the digits 0, 2, 3, 5 and 9.at n=39A136891
- Triangular numbers n*(n+1)/2 with n and n+1 composite, where number of prime factors in n = number of prime factors in n+1. (Prime factors are counted with multiplicity.)at n=38A144486
- Integer nearest f(2^n), where f(x) = Sum of ( mu(k) * H(k)/k^(3/2) * Integral Log(x^(1/k)) ) for k = 1 to infinity, where H(k) is the harmonic number Sum_{i=1..k} 1/i.at n=17A201542
- Triangular numbers of the form 2p-1 where p is prime.at n=28A217000
- Triangular numbers whose binary conversion, read in decimal, is prime.at n=9A227028
- Triangular numbers A000217 composed of only curved digits {0, 2, 3, 5, 6, 8, 9}.at n=38A247016
- Number of partitions of n in which the sequence of the sum of the same summands is nondecreasing.at n=50A304405
- Expansion of (-5*(9 - 6*x + 2*x^2))/(-1 + x)^3.at n=41A331190
- Triangular numbers (A000217) whose second arithmetic derivative (A068346) is also a triangular number.at n=39A351131