A135761 Natural numbers with every odd prime p swapped with p+1.

1, 2, 4, 3, 6, 5, 8, 7, 9, 10, 12, 11, 14, 13, 15, 16, 18, 17, 20, 19, 21, 22, 24, 23, 25, 26, 27, 28, 30, 29, 32, 31, 33, 34, 35, 36, 38, 37, 39, 40, 42, 41, 44, 43, 45, 46, 48, 47, 49, 50, 51, 52, 54, 53, 55, 56, 57, 58, 60, 59, 62, 61, 63, 64, 65, 66, 68, 67, 69, 70, 72, 71

Offset: 1

Author

Zak Seidov, Nov 27 2007

Keywords

• nonn

Examples

			Start with sequence of positive integers, then swap a(i) and a(i+1) if a(i) is an odd prime:
a(1)=1, a(2)=2, then a(3)=4 and a(4)=3 because p=3 is odd prime and p and p+1 are swapped.
		

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A135762.

Programs

Maple

f:= proc(n) if isprime(2*n+1) then (2*n+2,2*n+1) else (2*n+1,2*n+2) fi end proc:
map(f, [$0..100]); # Robert Israel, Nov 07 2016

Mathematica

r=Range[100];Do[If[PrimeQ[r[[i]]],{r[[i]],r[[i+1]]}={r[[i+1]],r[[i]]}],{i,3,97,2}];r