OFFSET
1,2
PROG
(PARI) is(n) = my(d = digits(n, 5), t=1, i); forstep(i=#d, 2, -1, if(d[i] * t > d[i-1] * t, return(0)); t=-t); 1 \\ David A. Corneth, Jan 29 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Clark Kimberling, corrected Jul 07 2000
STATUS
approved