A335331 a(n) = prime(k) where k is the n-th 7-smooth number.

2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 37, 43, 47, 53, 61, 71, 73, 89, 97, 103, 107, 113, 131, 149, 151, 173, 181, 197, 223, 227, 229, 251, 263, 281, 307, 311, 349, 359, 379, 409, 419, 433, 463, 503, 521, 541, 571, 593, 613, 659, 691, 701, 719, 761, 809, 827, 853, 863

Offset: 1

Author

David A. Corneth, Jun 01 2020

Keywords

• nonn

Comments

At A110069 we look for numbers of the form n = (d_1 + d_2 + ... + d_k)*prime(d_1*d_2*...*d_k) where d_1 d_2 ... d_k is the decimal expansion of n. As the largest prime that can be among the digits of a base-10 number is 7, the product of digits is 7-smooth. Hence the factor prime(d_1*d_2*...*d_k) is a term from this sequence. As lots of numbers have a product of digits of, say, 210^4, it would help to know prime(210^4) in advance. That's a(5817) of this sequence as 210^4 is the 5817th 7-smooth number. Precomputing such numbers is a computational benefit.

Links

• David A. Corneth, Table of n, a(n) for n = 1..8862

Crossrefs

Cf. A002473, A006988, A033844, A110069.