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A113604 Define f(k) = k + sum of digits of n. a(n) is the first prime that results by applying f zero or more times to n, or 0 if no such prime exists. 0

%I

%S 2,2,3,23,5,0,7,23,0,11,11,0,13,19,0,23,17,0,19,41,0,41,23,0,37,41,0,

%T 101,29,0,31,37,0,41,43,0,37,101,0,59,41,0,43,59,0,67,47,0,101,89,0,

%U 59,53,0,89,67,0,71,59,0,61,101,0,127,89,0,67,103,0,101,71,0,73,127,0,89

%N Define f(k) = k + sum of digits of n. a(n) is the first prime that results by applying f zero or more times to n, or 0 if no such prime exists.

%C a(n) = n for n prime; a(n) = 0 for n > 3 and n == 0 (mod 3).

%C Conjecture: a(n) = 0 only if n == 0 (mod 3).

%e a(4) = 23 since f(4) = 4+4 = 8, f(8) = 8+8 = 16, f(16) = 16+1+6 = 23.

%o (PARI) f(n) = local(k,s,d);k=n;s=0;while(k>0,d=divrem(k,10);k=d[1];s=s+d[2]);s+n {m=76;for(n=1,m,if(n>3&&n%3==0,print1(0,","),k=n;z=1000*n;while(k<z&&!isprime(k),k=f(k));print1(if(k<z,k,0),",")))}

%Y Cf. A113605.

%K base,easy,nonn

%O 1,1

%A _Amarnath Murthy_, Nov 09 2005

%E Edited and extended by _Klaus Brockhaus_, Nov 10 2005

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Last modified October 16 18:03 EDT 2019. Contains 328102 sequences. (Running on oeis4.)