23117

Properties

Appears in sequences

• a(n) = floor(Sum_{k=0..n} k!/2), or floor( A003422(n+1)/2 ).at n=8A014288
• a(n) = Sum_{k=0..n-1} T(n,k) * T(n,k+1), with T given by A026725.at n=7A027208
• Discriminants of real quadratic fields with class number 1 and related continued fraction period length of 15.at n=17A050964
• Primes which when added to their reversals are squares.at n=7A059799
• a(n) is the smallest number m such that m! is divisible by the left factorial !n (A003422).at n=8A062549
• Primes of the form x^2 + (x+3)^2.at n=24A076727
• Primes arising in A083758.at n=3A083759
• Triangle, read by rows, defined by: T(n,k) = (k+1)*T(n,k+1) - Sum_{j=1..n-k-1} T(j,0)*T(n,j+k+1) for n>k with T(n,n)=1 for n>=0.at n=37A117396
• Primes of the form !(k + 1)/2 = Sum_{i=0..k} i!/2.at n=4A124374
• Primes q such that p = (r+q+s-1)/2 is a balanced prime, where r, q, s are consecutive primes.at n=10A129190
• Primes of the form k^2 + 13.at n=27A138375
• Primes p such that continued fraction of (1 + sqrt(p))/2 has period 15: primes in A146338.at n=33A146360
• Triangle read by rows: a(1,1)=1. a(m,n) = a(m-1,n) + (sum of all terms in row m-1), for n<m. a(m,m) = sum of all terms in row m-1.at n=28A159930
• Numbers with d digits (d>0) which have at least 2d distinct primes as substrings.at n=19A168167
• a(n) = Sum_{k<=n} A007955(k) * A000027(k) = Sum_{k<=n} A007955(k) * k, where A007955(m) = product of divisors of m.at n=12A174935
• Primes with nine embedded primes.at n=7A179917
• Primes of the form 5n^2 - 3.at n=11A201785
• Number of (n+2) X 5 0..1 matrices with each 3 X 3 subblock idempotent.at n=16A224554
• Primes formed by concatenation (exponent then prime) of prime factorizations of the positive integers.at n=34A226095
• Number of (2+1)X(n+1) 0..1 arrays x(i,j) with row sums sum{j*x(i,j), j=1..n+1} nondecreasing, and column sums sum{i^2*x(i,j), i=1..2+1} nondecreasing.at n=11A233367