1,2

a(1) = round(1.0080) = 1 = mean atomic weight of hydrogen (protium + deuterium + tritium).

a(2) = round (1.0080+4.003) = round(5.011) = 5 (heium 4 and rarer helium 3).

Cf. A007656, A070217.

Sequence in context: A047077 A086570 A063559 this_sequence A097984 A028347 A038794

Adjacent sequences: A121288 A121289 A121290 this_sequence A121292 A121293 A121294

nonn

Jonathan Vos Post (jvospost3(AT)gmail.com), Aug 24 2006