A372075 a(1) = 1; thereafter a(n+1) is obtained by prepending the digit-sum of a(n) to a(n).
1, 11, 211, 4211, 84211, 1684211, 231684211, 28231684211, 3828231684211, 493828231684211, 62493828231684211, 7062493828231684211, 777062493828231684211, 91777062493828231684211, 10191777062493828231684211, 10310191777062493828231684211
Offset: 1
Examples
a(4) = 4211 as a(3) = 211 which has digital sum 2 + 1 + 1 = 4. Concatenating 4 and 211 gives 4211. - _David A. Corneth_, Jun 16 2024
Links
- Paolo Xausa, Table of n, a(n) for n = 1..270
Programs
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Mathematica
NestList[DigitSum[#]*10^IntegerLength[#] + # &, 1, 20] (* Paolo Xausa, Jun 16 2024 *)
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PARI
first(n) = { my(res = vector(n)); res[1] = 1; for(i = 2, n, res[i] = sumdigits(res[i-1])*10^(#digits(res[i-1]))+res[i-1] ); res } \\ David A. Corneth, Jun 16 2024 -
Python
from itertools import islice def A372075_gen(): # generator of terms yield (a:=1) while True: yield (a:=a+10**len(s:=str(a))*sum(map(int,s))) A372075_list = list(islice(A372075_gen(),20)) # Chai Wah Wu, Jun 16 2024