21179

Properties

Appears in sequences

• Primes of the form k^2 + k + 9.at n=17A027758
• Smallest number that can be made to take n steps to reach 0 under "k -> any product of 2 numbers whose concatenation is k".at n=22A035934
• Primes prime(k) for which A049076(k) = 4.at n=11A049080
• Primes for which A049076 >= 4.at n=19A049090
• Let Do(n) = A006566(n) = n-th dodecahedral number. Consider all integer triples (i,j,k), j >= k > 0, with Do(i) = Do(j) + Do(k), ordered by increasing i; sequence gives k values.at n=10A053019
• a(1) = 2, a(n) = concatenation of two closest factors of a(n-1) whose product equals a(n-1) or if a(n-1) is a prime then the concatenation of 1 and a(n-1).at n=8A062094
• a(n) = prime(2*n*(n+1)+1).at n=34A078746
• Primes of the form 4*k-1 such that 8*k-1 and 16*k-1 are also primes.at n=33A101791
• Primes p such that 2p+1, 4p+3, 6p+5 are all primes.at n=21A107020
• Primes congruent to 12 mod 61.at n=40A142810
• Primes of the form 7n^2 + 4.at n=15A201605
• Primes that are the sum of 51 consecutive primes.at n=13A215992
• Primes p of the form penta(n)-3, where penta(n) is the n-th pentagonal number.at n=29A232537
• 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=25A295013
• The number of partitions of n in which at least one part is a multiple of 4.at n=39A295342
• a(n) = n if n is 1 or prime; otherwise (1) let m = (concatenation of the two divisors in the middle of rows of A027750(n)), (2) if m is prime then a(n) = m, otherwise return to (1) with n=m.at n=11A329181
• a(n) = n if n is 1 or prime; otherwise (1) let m = (concatenation of the two divisors in the middle of rows of A027750(n)), (2) if m is prime then a(n) = m, otherwise return to (1) with n=m.at n=33A329181
• Prime numbers with prime indices in A333243.at n=14A333244
• Primes p such that p^7 - 1 has 8 divisors.at n=16A341669
• Prime numbersat n=2381