This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A383357 #25 May 09 2025 18:48:55
%S A383357 1,2,4,20,34,35,77,158,181,401,973,3517,6818
%N A383357 Integers m such that R(Sum_{k=1..m} (10^k+k)) is prime, where R is the digit reversal function A004086.
%C A383357 The primes referred to in the above definition consist, after the rightmost few digits >= 1, of only 1's and their size increases quickly with m as shown below.
%C A383357 m Primes Number of digits of primes
%C A383357 ---------------------------------------------------------------
%C A383357 1 11 2
%C A383357 2 311 3
%C A383357 4 2111 4
%C A383357 20 23111..1 21
%C A383357 . . .
%C A383357 . . .
%C A383357 401 11719111..1 402
%C A383357 973 169485111..1 974
%C A383357 3517 3157927111..1 3518
%C A383357 6818 18075343111..1 6819
%C A383357 .
%C A383357 .
%C A383357 If it exists a(14), >= 10^4.
%e A383357 1 is a term because 10^1+1 = 11 and its digit reversal is 11, which is prime.
%e A383357 2 is a term because 10^1+1 + 10^2+2 = 113 and its digit reversal is 311, a prime.
%e A383357 3 is not a term because 10^1+1 + 10^2+2 + 10^3+3 = 1116 and R(1116) = 6111, not prime.
%o A383357 (PARI) for(n=1,400,my(s=fromdigits(Vecrev(digits(sum(k=1,n,10^k+k)))));if(ispseudoprime(s),print1(n", ")));
%Y A383357 Cf. A000040, A004086, A073805.
%K A383357 nonn,base,more
%O A383357 1,2
%A A383357 _Claude H. R. Dequatre_, Apr 24 2025