113435141domain: NPropertiesPrimalityPrimeyesAppears in sequencesLet S(1)={1} and, for n>1 let S(n) be the smallest set containing x, x+1, 2x and 3x for each element x in S(n-1). a(n) is the number of elements in S(n).at n=26A123247Prime numbersat n=6488546