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

1,2

Links

Paolo Xausa, Table of n, a(n) for n = 1..270

Example

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

Mathematica

NestList[DigitSum[#]*10^IntegerLength[#] + # &, 1, 20] (* Paolo Xausa, Jun 16 2024 *)

Prog

(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

Crossrefs

Cf. A004207, A007953, A372074.

Sequence in context: A053582 A077714 A089567 * A110747 A112704 A243674

Adjacent sequences: A372072 A372073 A372074 * A372076 A372077 A372078

Keyword

nonn,base

Author

N. J. A. Sloane, Jun 16 2024

Status

approved