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a(1) = 221 because this is the first squarefree composite number n such that exactly two integers b except 0 exist such that for every prime factor p of n applies that , p+b divides n+b (-11, -5): 221=13*17 and 2, 6 both divide 210 and 8, 12 both divide 216.
reviewed
editing
proposed
reviewed
editing
proposed
a(1) = 221 because this is the first squarefree composite number n such that exactly two integers b except 0 exist such that for every prime factor p of n applies that p+b divides n+b (-11, -5): 221=13*17 and 2, 6 both divide 210 and 8, 12 both divide 216.
a(1) = 221 because this is the first squarefree composite number n such that exactly two integers except 0 exist such that for every prime factor p of n applies that p+b divides n+b (-11, -5): 221=13*17 and 2, 6 both divides divide 210 and 8, 12 both divides divide 216.
a(1) = 221 because this is the first squarefree composite number n such that exactly two integers except 0 exist such that for every prime factor p of n applies that p+b divides n+b (-11, -5): 221=13*17 and 2, 6 both divides 210 and 8, 12 both divides 216.
Tim Johannes Ohrtmann, <a href="/A257752/b257752.txt">Table of n, a(n) for n = 1..1487</a>