A375507 - OEIS

%I #23 Aug 20 2024 16:06:01

%S 1,2,14,135,1349,13490,134903,1349038,13490389,134903902,1349039036,

%T 13490390385,134903903876,1349039038789,13490390387923,

%U 134903903879272,1349039038792762,13490390387927663,134903903879276676,1349039038792766810,13490390387927668159

%N a(1) = 1. For n > 1; a(n) is equal to a(n-1) plus the decimal value of the concatenation of the first n-1 digits of the sequence.

%F a(n) ~ (c/9)*10^(n-1), where c = Sum_{n>=1} a(n)/10^(n*(n-1)/2) = 1.2141351349... . - _Pontus von Brömssen_, Aug 18 2024

%e For n = 4 we have that a(n-1) = a(3) = 14 and the decimal value of the concatenation of the first three digits of the sequence is 121, so a(4) = 14 + 121 = 135.

%o (Python)

%o from itertools import count

%o def A375507_list(nmax):

%o     a = [1]

%o     def digits():

%o         for i in count():

%o             for d in str(a[i]):

%o                 yield int(d)

%o     diff = 0

%o     for n,d in enumerate(digits(),1):

%o         if n==nmax: return a

%o         diff = 10*diff+d

%o         a.append(a[-1]+diff) # _Pontus von Brömssen_, Aug 18 2024

%K nonn,base

%O 1,2

%A _Rodolfo Kurchan_, Aug 18 2024

%E a(17)-a(21) from _Pontus von Brömssen_, Aug 18 2024