A244599 Least primes x that remain primes for n steps under the transform T(x) as defined in A243993.

2, 29, 227, 22807, 86269, 2206031, 668880743, 4208046655963

Offset

0,1

Comments

Only primes with most significant digit even.

Links

Table of n, a(n) for n=0..7.

Example

n=0: 2
n=1: 29 -> 11
n=2: 227 -> 499 -> 383
n=3: 22807 -> 40879 -> 48563 -> 23197
n=4: 86269 -> 48857 -> 26321 -> 89533 -> 74861
n=5: 2206031 -> 4266343 -> 6829777 -> 4016443 -> 4170877 -> 5878541
n=6: 668880743 -> 246687179 -> 602458861 -> 626936477 -> 885290143 -> 637191571 -> 908006287
n=7: 4208046655963 -> 6288402104597 -> 8062423149463 -> 8686654533091 -> 4442199863909 -> 8863087492993 -> 6493851311821 -> 321364429037.

Maple

with(numtheory);
T:=proc(t) local j, w, x, y; x:=t; y:=[]; while x>0 do
y:=[x mod 10, op(y)]; x:=trunc(x/10); od; w:=(y[nops(y)]+y[1]) mod 10;
x:=0; for j from 1 to nops(y)-1 do x:=x*10+((y[j]+y[j+1]) mod 10); od; x:=x*10+w; end:
P:=proc(q) local a, b, n, v; v:=array(0..50);
for n from 0 to 50 do v[n]:=0; od; v[0]:=2; lprint(0, 2);
for n from 1 by 2 to q do if isprime(n) then b:=-1; a:=n;
while isprime(a) do b:=b+1; a:=T(a); od; if v[b]=0 then
v[b]:=n; lprint(b, n); fi; fi; od; end: P(10^10);

Crossrefs

Cf. A243993.

Sequence in context: A179024 A179025 A377627 * A261268 A020460 A178000

Adjacent sequences: A244596 A244597 A244598 * A244600 A244601 A244602

Keyword

nonn,more

Author

Paolo P. Lava, Jul 01 2014

Extensions

a(7) from Giovanni Resta, Jul 03 2014

Status

approved