21341

Properties

Appears in sequences

• Numbers k such that the continued fraction for sqrt(k) has period 93.at n=19A020432
• 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 58.at n=1A031646
• Define an increasing sequence as follows. Given the first term called the seed (the seed need not have the property of the sequence.). Subsequent terms are defined as obtained by inserting/placing digits (at least one) in the previous term to obtain the smallest number with a given property. This is the growing prime sequence for the seed a(1) = 4.at n=4A068169
• Numerator of Sum_{1<k<n, n mod k > 0} n/k.at n=11A079076
• a(1) = 2 then primes in nondecreasing order such that every concatenation is prime.at n=37A089702
• Primes whose decimal representation is a valid number in base 5 and interpreted as such is again a prime.at n=34A090708
• Right truncatable primes in base 9 (written in decimal form).at n=43A129693
• Primes congruent to 52 mod 61.at n=39A142850
• Primes p0 such that p0+p1+p2-+2 are primes; p0,p1,p2 are three consecutive primes.at n=21A158351
• Number of binary strings of length n with equal numbers of 0000 and 0011 substrings.at n=16A164149
• Smallest primes p = p(k) with (p(k)+p(k+1)+p(k+2))/15 an integer.at n=14A168556
• a(n) = b_n(p_(n+1)) where p_n is the n-th prime, b_n(1)=1, b_n(2)=p_n, and for k>=3, b_n(k) is the smallest number larger than b_n(k-1) such that, for all i<k, b_n(k) is relatively prime to b_n(i) iff k is relatively prime to i.at n=7A173381
• Numerator of sum of reciprocals of numbers less than n that do not divide n.at n=11A281085
• Prime time primes on 6-digit clocks, second definition: primes of the form HMMSS where H, MM, SS are primes, H < 24, MM and SS < 60.at n=30A295013
• Primes of the form k^2 + 25.at n=34A346145
• Primes p such that p+1 is a triprime and 2*p+1 is prime.at n=38A386295
• Lesser of sexy happy primes.at n=30A387258
• a(1)=2; thereafter a(n) = a(n-1) + gpf(a(n-1)) - 1, where gpf = greatest prime factor = A006530.at n=33A389408
• Prime numbersat n=2396