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.
A127889=vector(8, n, p=concat(apply(t->primes([t, t+1]*10), if(n>1, p))); p[1]) \\ M. F. Hasler, Nov 07 2018
a(4) = 1223 in which the four substrings containing the LSD (3,23,223,1223) are primes.
f(n, d, digs, spare) = local(p, r, found); if (!d, return(n)); found = 0; for (i = 0, 9, p = n + i*10^digs; if ((i && isprime(p)) || spare, r = f(p, d - 1, digs + 1, spare - 1 + (i && isprime(p)))); if (r && (r < found || !found), found = r)); found; a(n) = local(i, r); i = 0; while (1, r = f(0, n + i, 0, i); if (r, return(r), i++)); \\ David Wasserman, Aug 12 2005
a(1)=2 a(2)=23 a(3)=233 a(4)=2333 a(5)=23333
a(6) = 2333323 since a(5) = 23333 (prime) and 233333, 233335, 233337, 2333311, 2333313, 2333317 and 2333319 are all composite.
nxt[n_]:=Module[{k=3},While[CompositeQ[n*10^IntegerLength[k]+k],k = NextPrime[ k]];n*10^IntegerLength[k]+k]; NestList[nxt,2,20] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 13 2019 *)
from itertools import islice
from sympy import isprime, nextprime
def agen(): # generator of terms
p, s = 2, "2"
while True:
yield p
q = 2
while not isprime(p:=int(s+str(q))):
q = nextprime(q)
s += str(q)
print(list(islice(agen(), 15))) # Michael S. Branicky, May 26 2023
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