A187553 - OEIS

%I #13 Mar 30 2012 18:35:54

%S 0,11,0,2,101111,211,2111,101111111,3,13,113,112121,23,21221,1123,

%T 11213,41,1223,313,10133,241,233,112223,21313,5,431,151,1151,13313,

%U 251,2333,11251,2243,53,1433,1153,61,523,1523,11161,443,541,353,33413,2621,163,1163,13523,7,17

%N Smallest prime p such that the sum of the squares of the digits of p equals n (or 0 if no such prime exists).

%C a(3) = 0 because the numbers of the form 10..010..01 are divisible by 3. Conjecture : except for the numbers 1 and 3, for every possible square digit sum there exists a prime.

%e a(13) = 23 because 2^2 + 3^2 = 13, and 23 is the least such prime.

%p with(numtheory):for k from 2 to 100 do: id:=0:for p from 1 to 100000 while(id=0)

%p   do:n:=ithprime(p):l:=length(n):n0:=n:s:=0:for m from 1 to l do:q:=n0:u:=irem(q,10):v:=iquo(q,10):n0:=v :s:=s+u^2:od: if s=k then id:=1:printf(`%d, `,n):else fi:od:od:

%Y Cf. A003132, A020449, A055016, A067180.

%K nonn,base

%O 1,2

%A _Michel Lagneau_, Mar 26 2011