1,1

3(=0+1+2=sum_{x=0..2} x), 6(=1+2+3=sum_{x=1..3} x), 9(=4+5=Sum_{x=4..5} x), 13(=6+7=Sum_{x=6..7} x), 38(=8+9+10+11=Sum_{x=8..11} x), etc.

Cf. A000040, A141468.

Sequence in context: A137041 A153006 A086838 this_sequence A128261 A000791 A027424

Adjacent sequences: A161666 A161667 A161668 this_sequence A161670 A161671 A161672

nonn

Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Jun 16 2009, Jun 27 2009