OFFSET
1,1
COMMENTS
More than the usual number of terms are shown in order to distinguish this from neighboring sequences.
The definition as it stands would also include single-digit numbers. The nontrivial terms are those with more than 2 digits. - M. F. Hasler, Oct 08 2019
REFERENCES
Eric Angelini, Posting to Sequence Fans Mailing List, Oct 07 2019.
LINKS
Eric Angelini and Jean-Marc Falcoz, Table of n, a(n) for n = 1..1862 (The complete list of terms)
EXAMPLE
The 2-digit absolute differences of 1862 are 7,5,1,2,6,4, all different, so 1862 is a term (and also the number of terms).
PROG
(PARI) select( is(n)={n<99||#Set(abs(concat(vector(-1+#n=digits(n), k, n[1..k]-vector(k, i, 1)*n[k+1]))))*2==#n*(#n-1)}, [1..9999]) \\ M. F. Hasler, Oct 08 2019
CROSSREFS
KEYWORD
nonn,base,fini
AUTHOR
N. J. A. Sloane, Oct 07 2019
STATUS
approved