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A335331
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a(n) = prime(k) where k is the n-th 7-smooth number.
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2
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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
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OFFSET
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1,1
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COMMENTS
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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.
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LINKS
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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