A244433 a(n) is the smallest number m such that 2im+1 is composite for all i, 0

4, 12, 19, 19, 59, 92, 159, 159, 159, 227, 227, 256, 256, 256, 514, 514, 706, 706, 706, 706, 706, 706, 706, 1466, 1466, 1466, 1466, 1466, 1466, 5207, 5207, 5207, 5207, 5207, 5207, 5207, 5207, 5207, 5207, 5207, 5207, 21209, 21209, 21209, 21209, 21209, 21209, 21209, 21209, 21209, 21209, 21209, 21209, 62809, 62809, 62809, 86914, 86914, 86914, 152351

Offset: 1

Author

Farideh Firoozbakht, Jul 18 2014

Keywords

• nonn

Comments

a(3)=a(4)=19, a(7)=a(8)=a(9)=159, ..., a(74)=a(75)=...=a(82)=424783, ... . A244434 gives numbers n such that a(n) does not belong to the set {a(n-1),a(n+1)}.

Examples

			a(3)=19 because all the three numbers 2*1*19+1=39, 2*2*19+1=77 & 2*3*19+1=115 are composite and 19 is the smallest such number.
		

Crossrefs

Cf. A071576, A244434, A244435.