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

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

1,1

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)}.

Links

Table of n, a(n) for n=1..60.

Example

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.

Sequence in context: A177833 A166162 A228166 * A086109 A275116 A139388

Adjacent sequences: A244430 A244431 A244432 * A244434 A244435 A244436

Keyword

nonn

Author

Farideh Firoozbakht, Jul 18 2014

Status

approved