A342958 a(n) is the least prime that starts a string of exactly n primes p_1, p_2, ... p_n where p_{i+1} = p_i-A003132(p_i), but p_n-A003132(p_n) is not prime.

2, 13, 547, 10559, 246349, 20020109, 20020163

Offset: 1

Author

J. M. Bergot and Robert Israel, Mar 31 2021

Keywords

• nonn
• more
• base

Comments

No further terms < 10^9.

Examples

			a(3) = 547 because 547, 547-A003132(547) = 457, and 457-A003132(457) = 367 are prime, but 367-A003132(367) = 273 is not prime.
		

Crossrefs

Cf. A003132, A179549, A342953.

Programs

Maple

f:= proc(n) option remember; local t, x;
  x:= n - add(t^2, t=convert(n, base, 10));
  if not isprime(x) then 1 else 1+procname(x) fi
end proc:
V:= Vector(7): count:= 0: p:= 1:
while count < 7 do
  p:= nextprime(p); v:= f(p);
  if v <= N and V[v] = 0 then V[v]:= p; count:= count+1 fi
od:
convert(V, list);