OFFSET
1,2
REFERENCES
Clifford A. Pickover, Wonders of Numbers, Oxford University Press, NY, 2001, p. 185-186.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Clifford A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review.
FORMULA
Ulam numbers are positive integers that can be expressed in just one way as the sum of two distinct earlier members of the sequence in increasing order.
EXAMPLE
a(4) = 11 is an Ulam number because 10 + 1 = 11, but 19 is not because there is more than one way to form 19 from summing previous sequence numbers, e.g., 18 + 1 and 10 + 9.
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jason Earls, Mar 16 2001
STATUS
approved