OFFSET
1,2
LINKS
A. Cobham, Uniform Tag Sequences, Mathematical Systems Theory, 6 (1972), 164-192.
FORMULA
a(n) = Sum_{i=1..n} A000030(i). a(n) = Sum_{i=1..n} [i / 10^([log_10(i)])] where [] denotes floor and log_10(i) is the logarithm is base 10. a(n+1) = a(n) + first-digit-of(n+1).
MATHEMATICA
f[n_] := Sum[ Floor[i / 10^Floor[Log[10, i]]], {i, n}]; Table[ f[n], {n, 62}] (* or *)
a[0] = 0; a[n_] := a[n] = (a[n - 1] + First[ IntegerDigits[ n]]); Table[ a[n], {n, 62}] (* Robert G. Wilson v, Aug 30 2005 *)
Accumulate[First/@(IntegerDigits/@Range[70])] (* Harvey P. Dale, Jan 11 2016 *)
PROG
(PARI) a(n) = sum(k=1, n, digits(k)[1]); \\ Michel Marcus, Dec 13 2017
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Jonathan Vos Post, Aug 27 2005
EXTENSIONS
Corrected by Robert G. Wilson v, Aug 30 2005
STATUS
approved