19253

Appears in sequences

• a(1)=4, then least semiprime > a(n-1) such that when all in the sequence are concatenated together they form a prime.at n=38A085703
• a(n) = least k such that the remainder when 28^k is divided by k is n.at n=44A128368
• Row sums from A144562.at n=25A144640
• Number of non-equivalent ways (mod D_2) to select 4 points from n equidistant points on a straight line so that no selected point is equally distant from two other selected points.at n=30A300761
• a(n) = Sum_{k=0..n} (-1)^k * binomial(2*n+k-1,k) * binomial(6*n-k-1,n-k).at n=5A370104