A174214 a(n) = a(n-1)+1, if the previous term a(n-1) and n-1-(-1)^n are coprime, else a(n)=2*n-4.

14, 16, 17, 18, 19, 20, 26, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 52, 53, 54, 55, 60, 62, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134

Offset: 9

Author

Vladimir Shevelev, Mar 12 2010

Keywords

• nonn
• easy

Links

• V. Shevelev, Theorems on twin primes-dual case, arXiv:0912.4006 [math.GM], 2009-2014.

Crossrefs

Cf. A166945, A167495.

Programs

Maple

A174214 := proc(n) option remember ; if n = 9 then 14 ; elif gcd(procname(n-1),n-1-(-1)^n) = 1 then procname(n-1)+1 ; else 2*n-4 ; end if; end proc:
seq(A174214(n),n=9..100) ; # R. J. Mathar, Mar 16 2010

Mathematica

a[n_] := a[n] = Which[n==9, 14, CoprimeQ[a[n-1], n-1-(-1)^n], a[n-1]+1, True, 2n-4]; Table[a[n], {n, 9, 100}] (* Jean-François Alcover, Feb 02 2016 *)

Extensions

a(15) corrected and sequence extended by R. J. Mathar, Mar 16 2010

a(15) corrected and a(35)-a(74) added by John W. Layman, Mar 16 2010