A236672 Start with 9; thereafter, primes obtained by concatenating to the end of previous term the next smallest number that will produce a prime.
9, 97, 971, 9719, 971917, 97191713, 9719171333, 971917133323, 9719171333237, 971917133323777, 97191713332377731, 9719171333237773159, 971917133323777315951, 97191713332377731595127, 971917133323777315951277, 971917133323777315951277269
Offset: 1
Examples
a(1) = 9 by definition. a(2) is the next smallest prime beginning with 9, so a(2) = 97. a(3) is the next smallest prime beginning with 97, so a(3) = 971.
Links
- Robert Israel, Table of n, a(n) for n = 1..316
Programs
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Maple
R:= 9: x:= 9: for i from 2 to 20 do for y from 1 by 2 do z:= x*10^(1+ilog10(y)) + y; if isprime(z) then R:= R,z; x:= z; break fi od od: R; # Robert Israel, Nov 22 2023 -
Mathematica
next[p_]:=Module[{i=1,q},While[!PrimeQ[q=10^IntegerLength[i]p+i],i+=2];q]; NestList[next,9,15] (* Paolo Xausa, Nov 23 2023 *) -
Python
import sympy from sympy import isprime def b(x): num = str(x) n = 1 while n < 10**3: new_num = str(x) + str(n) if isprime(int(new_num)): print(int(new_num)) x = new_num n = 1 else: n += 1 b(9)
Comments