1,2

For n>1, A103839(n)=2*A051239(n).

For n = 5, we have the 4 permutations and the sums of adjacent elements:

1,4,3,2,5 (1+4=5, 4+3=7, 3+2=5, 2+5=7)

3,4,1,2,5 (3+4=7, 4+1=5, 1+2=3, 2+5=7)

5,2,1,4,3 (5+2=7, 2+1=3, 1+4=5, 4+3=7)

5,2,3,4,1 (5+2=7, 2+3=5, 3+4=7, 4+1=5)

Sequence in context: A144847 A143625 A003612 this_sequence A135727 A075101 A075103

Adjacent sequences: A103836 A103837 A103838 this_sequence A103840 A103841 A103842

nonn

N. J. A. Sloane (njas(AT)research.att.com), Mar 30 2005

More terms from Max Alekseyev, Jan 04 2008