cp's OEIS Frontend

A229222 Smallest prime p such that p contains a digit larger than 1 and the sum of the n-th powers of the decimal digits of p is a prime number.

%I A229222 #19 Sep 20 2013 10:46:03
%S A229222 2,23,113,23,191,223,191,41,223,113,157,191,137,113,113,43,137,191,
%T A229222 179,337,577,223,227,113,263,113,199,229,263,199,467,89,223,179,223,
%U A229222 113,443,683,1279,337,661,463,827,2281,577,223,223,661,137,229,11399,461,577
%N A229222 Smallest prime p such that p contains a digit larger than 1 and the sum of the n-th powers of the decimal digits of p is a prime number.
%C A229222 We impose the condition that p is not in A020449 in order to avoid trivial sequences with infinite repetitions with the numbers 11 if p>1, or 101 if p>11, or 101111 if p > 101, ... for example if p > 1 the sequence is {2, 11, 11, 11, ...}, if p > 11 the sequence is {23, 23, 101, 23, 101, 101, 41, 101, 101, 101, 101, 101, ...}.
%C A229222 a(n) is an unification of a family of sequences mentioned hereafter:
%C A229222 A082101: primes of the form 2^n+3^n => 23 is in the sequence;
%C A229222 A057735: primes of the form 3^n+2 => 113 is in the sequence;
%C A229222 A153133: primes of the form 2^n+3^(n-1) => 223 is in the sequence;
%C A229222 A228034: primes of the form 9^n+2 => 191 is in the sequence;
%C A229222 A057733: primes of the form 2^n+3 => 2111 is in the sequence;
%C A229222 A228026: primes of the form 4^n+3 => 4111 is in the sequence;
%C A229222 A228034: primes of the form 9^n+2 => 191 is in the sequence;
%C A229222 A182330: primes of the form 5^n+2 => 151 is in the sequence;
%C A229222 A111974: primes of the form 2*3^n+1 => 313 is in the sequence;
%C A229222 A102903: primes of the form 3^n+4 => 11113 is in the sequence.
%C A229222 In this sequence, we observe repetitions of numbers such that 23, 113, 223, 191, 199, 223,... and this problem is very difficult, because it is probable that there exists both finite and infinite repetitions according to the numbers: for example, if we consider the number 23 of this sequence, it is probable that the number of element "23" is finite (see the comment in A082101 for the primes of form 2^k + 3^k). But, if we consider the number 113 of this sequence, is the number of the elements "113" infinite ? (see A057735 with the primes of the form 2+3^n). We observe that a(n) = 113 for n = 3, 14, 15, 24, 26,..., 123, 126, 139,..., 386, 391, 494, ....
%H A229222 Michel Lagneau, <a href="/A229222/b229222.txt">Table of n, a(n) for n = 1..500</a>
%e A229222 a(3) = 113 because 1^3+1^3+3^3 = 29 is prime.
%p A229222 with(numtheory) :lst:={11, 101, 101111, 10011101, 10101101, 10110011, 10111001, 11000111, 11100101, 11110111, 11111101 }:for n from 1 to 300 do :ii:=0:for k from 1 to 10^8 while(ii=0) do:x:=convert(k,base,10):n1:=nops(x):it:=0:jj:=0:s:= sum('x[i]^n', 'i'=1..n1):lst1:={k} intersect lst:if type(k,prime)=true and type(s,prime)=true and (lst1<>{k}) then ii:=1: printf(`%d, `,k):else fi:od:od:
%t A229222 Table[p = 2; While[d = IntegerDigits[p]; Union[d][[-1]] < 2 || ! PrimeQ[Total[d^n]],  p = NextPrime[p]]; p, {n, 60}]
%o A229222 (PARI) a(n)=forprime(p=2,,my(d=digits(p)); if(vecmax(d)>1 && isprime(sum(i=1,#d,d[i]^n)), return(p))) \\ _Charles R Greathouse IV_, Sep 19 2013
%Y A229222 Cf. A020449.
%K A229222 nonn,base
%O A229222 1,1
%A A229222 _Michel Lagneau_, Sep 16 2013