OFFSET
1,4
COMMENTS
In the prime factorization of k=A002808(i), i=1,2,3,..., one instance of the largest prime, pmax=A052369(i), is replaced by pmax-2 and one instance of the smallest prime, pmin=A056608(i), is replaced by pmin-1. If the product of this modified set of factors, k*(pmax-2)*(pmin-1)/(pmin*pmax), is nonprime, it is a term of the sequence.
EXAMPLE
composite k transformed product
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4 = 2*2 (2-1)*(2-2) = 1*0 = 0 = a(1)
6 = 2*3 (2-1)*(3-2) = 1*1 = 1 = a(2)
8 = 2*2*2 (2-1)*2*(2-2) = 1*2*0 = 0 = a(3)
9 = 3*3 (3-1)*(3-2) = 2*1 = 2 (prime)
10 = 2*5 (2-1)*(5-2) = 1*3 = 3 (prime)
12 = 2*2*3 (2-1)*2*(3-2) = 1*2*1 = 2 (prime)
14 = 2*7 (2-1)*(7-2) = 1*5 = 5 (prime)
15 = 3*5 (3-1)*(5-2) = 2*3 = 6 = a(4)
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Aug 08 2008
EXTENSIONS
Definition rephrased by R. J. Mathar, Aug 14 2008
Example section edited by Jon E. Schoenfield, Feb 20 2021
STATUS
approved