1,2

Mass number of the most abundant of the stable nuclids with atomic number equal to n. If there is no stable isotope, chose the one with the longest decay time.

Sequence is not well-defined, since the entries may change as more properties of the elements are discovered.

Moss and Winter give the atomic weight for Dysprosium (Dy) as "162.50(3)"; rounded to 163 rather than 162.

Bentor, Winter and Moss all give 145 as the atomic weight of the most stable isotope of Promethium (Pm), as opposed to 147 which was in the original data (between 144 and 150)

The largest-numbered element in the sequence is now element 114, Ununquadium (Uuq), with an atomic weight of 289 for the most stable isotope.

Also referred to as the mass number A of the most abundant and stable nuclide with atomic number Z=n. We have A = Z + N, where N is the neutron number A058317(n). - Lekraj Beedassy (blekraj(AT)yahoo.com), Oct 08 2005

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

CRC Handbook of Chemistry and Physics.

Y. Bentor, Chemical Elements.Com

R. B. Firestone & L. P. Ekstrom, Table of Radioactive Isotopes

G. P. Moss, Atomic Weights of the Elements 1999

M. Winter, WebElements Periodic Table

Author?, Accurate Masses and natural abundance of isotopesBased on 12C = 12.00000000.

Needs["Miscellaneous`ChemicalElements`"]; Table[ Round[ AtomicWeight[ Elements[[n]]]], {n, 1, 105}] (* above element 105, the values differ *)

Sequence in context: A153001 A010454 A053169 this_sequence A159619 A131827 A035245

Adjacent sequences: A007653 A007654 A007655 this_sequence A007657 A007658 A007659

nonn,uned,fini

N. J. A. Sloane (njas(AT)research.att.com).

More terms from Andre Engels (engels(AT)win.tue.nl)

Further terms from Philip Newton (pne(AT)writeme.com), Oct 26 2001, using data from Moss.

Comments from David Terr (davidcterr(AT)aol.com): There are several errors in this sequence. It looks to me that the rounded atomic weights were used rather than the mass number of the most abundant of the stable nuclides with atomic number equal to n. Thus for instance, a(28) should be 58, not 59 and a(29) should be 63, not 64. In fact, in all cases the parity of a(n) should be the same as n (both odd or both even). - David Terr (davidcterr(AT)aol.com), Oct 05 2006

I fixed all the entries I could find in which a(n) was incorrect, based on the online table of isotopic abundances at http://www.sisweb.com/referenc/source/exactmas.htm. - David Terr (davidcterr(AT)aol.com), Apr 06 2009

a(n) has the same parity as n for all stable elements except beryllium (n=4, a(n)=9), nitrogen (n=7, a(n)=14) and platinum (n=78, a(n)=195). [From David Terr (davidcterr(AT)aol.com), Apr 07 2009]