A175305 a(1)=1. a(n) = the smallest integer > a(n-1) where both a(n)-1 and a(n)+1 are coprime to all earlier terms of the sequence.

1, 2, 4, 6, 12, 18, 24, 30, 42, 60, 72, 102, 108, 138, 150, 168, 180, 192, 198, 228, 240, 270, 282, 312, 348, 420, 432, 462, 522, 570, 600, 618, 642, 660, 810, 822, 828, 858, 882, 1020, 1032, 1050, 1062, 1092, 1152, 1230, 1278, 1290, 1302, 1320, 1368, 1428

Offset

1,2

Comments

Every term from a(4) on is a multiple of 6.

Links

Table of n, a(n) for n=1..52.

Maple

A175305 := proc(n) option remember ; local wrks ; if n = 1 then 1; else for a from procname(n-1)+1 do wrks := true; for i from 1 to n-1 do if gcd(a-1, procname(i)) <> 1 or gcd(a+1, procname(i)) <> 1 then wrks := false; end if; end do: if wrks then return a; end if; end do: end if; end proc: seq(A175305(n), n=1..80) ; # R. J. Mathar, Apr 15 2010

Crossrefs

Sequence in context: A331091 A072121 A349179 * A342702 A171923 A060735

Adjacent sequences: A175302 A175303 A175304 * A175306 A175307 A175308

Keyword

nonn

Author

Leroy Quet, Apr 11 2010

Extensions

More terms from R. J. Mathar, Apr 15 2010

Status

approved