A121818 Average of atomic weights of all isotopes of first n elements, rounded to nearest integer.

1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 23, 24, 25, 26, 27, 28, 30, 31, 32, 33, 34, 35, 36, 38, 39, 40, 41, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 55, 56, 57, 58, 60, 61, 62, 63, 65, 66, 67, 69, 70, 71, 72, 74, 75, 76, 78, 79, 80, 81, 83, 84, 85

Offset

1,2

Comments

This is poorly defined, even with the caveats of A007656, for the highest atomic numbers (with no stable isotopes) and the values given are with respect to Earth, as different planets presumably have slightly different isotopic ratios.

Links

Table of n, a(n) for n=1..72.

Example

a(1) = round(1.0080/1) = 1 = mean atomic weight of hydrogen (protium + deuterium + tritium).
a(2) = round((1.0080+4.003)/2) = round(5.011/2) = round(2.5055) = 3.

Mathematica

Needs["Miscellaneous`ChemicalElements`"]
Table[ Round[ Sum[ AtomicWeight(AT)Elements[[i]], {i, n}]/n], {n, 111}] (* Robert G. Wilson v, Sep 02 2006 *)

Crossrefs

Cf. A007656, A070217, A121291.

Sequence in context: A081311 A366935 A053233 * A179005 A026505 A029674

Adjacent sequences: A121815 A121816 A121817 * A121819 A121820 A121821

Keyword

nonn,fini,less

Author

Jonathan Vos Post, Aug 26 2006

Extensions

More terms from Robert G. Wilson v, Sep 02 2006

Edited by N. J. A. Sloane, Sep 14 2006

Status

approved