A091780 - OEIS

A091780

Alternately odd and even numbers such that a(n) is the least number not included earlier and has a common factor with a(n-1).

3, 6, 9, 12, 15, 10, 5, 20, 25, 30, 21, 14, 7, 28, 35, 40, 45, 18, 27, 24, 33, 22, 11, 44, 55, 50, 65, 26, 13, 52, 39, 36, 51, 34, 17, 68, 85, 60, 57, 38, 19, 76, 95, 70, 49, 42, 63, 48, 69, 46, 23, 92, 115, 80, 75, 54, 81, 66, 77, 56, 91, 78, 87, 58, 29, 116, 145, 90, 93, 62

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OFFSET

1,1

COMMENTS

The sequence contains all the numbers except powers of 2.

LINKS

Table of n, a(n) for n=1..70.

MAPLE

A091780 := proc(nmax) local a, nstrt; a := [3] ; while nops(a) < nmax do if nops(a) mod 2 = 0 then nstrt := 5; else nstrt := 4 ; fi ; while nstrt in a or gcd(nstrt, op(-1, a)) < 2 do nstrt := nstrt+2 ; od ; a := [op(a), nstrt] ; od ; a ; end: A091780(80) ; # R. J. Mathar, Jul 26 2007

CROSSREFS

Sequence in context: A288522 A226894 A359213 * A331060 A329514 A346951

Adjacent sequences: A091777 A091778 A091779 * A091781 A091782 A091783

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Feb 16 2004

EXTENSIONS

More terms from R. J. Mathar, Jul 26 2007

STATUS

approved