A224827 - OEIS

%I #30 Apr 03 2023 10:36:13

%S 64279,64319,64483,64513,64621

%N Primes p such that prime(floor(p/10) + (p mod 10)) = p.

%C Subset of A224843. Sequence is clearly finite, since the ratio prime(n)/n is unbounded. By comparing prime(x/10) with x and using suitable functions which provide upper and lower bounds for prime(x), it is also possible to infer that no more terms exist. - _Giovanni Resta_, Jul 22 2013

%H Chris K. Caldwell and G. L. Honaker, Jr., <a href="https://t5k.org/curios/page.php?short=64621">Prime Curios! 64621</a>

%e prime(6462+1) = 64621 which is prime. Hence, 64621 is in sequence.

%p with(numtheory):KD := proc(p)

%p     ithprime((p-(p mod 10))/10 + (p mod 10))=p ;

%p end proc:

%p for p from 1 to 65000 do

%p     if KD(p) then

%p         printf("%d, ", p) ;

%p     end if;

%p end do:# _K. D. Bajpai_, Jul 21 2013

%p with(numtheory):K:=proc()local n,a,c,p;p:=3;c:=1;for n from 1 to 50000 do; p:=ithprime(n); a:= ithprime((p-(p mod 10))/10 + (p mod 10));if  p=a  then lprint(c,p); c:=c+1; fi;od; end: K(); # _K. D. Bajpai_, Jul 21 2013

%o (PARI) is(p)=p==prime(p\10+p%10)&&isprime(p) \\ _Charles R Greathouse IV_, Jul 22 2013

%Y Cf. A224843.

%K nonn,base,fini,full

%O 1,1

%A _K. D. Bajpai_, Jul 21 2013