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A093338 Scan primes, write down initial digit if it is a prime. 0

%I

%S 2,3,5,7,2,2,3,3,5,5,7,7,7,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3,3,3,3,3,

%T 3,3,3,3,3,3,3,3,3,3,3,5,5,5,5,5,5,5,5,5,5,5,5,5,5,7,7,7,7,7,7,7,7,7,

%U 7,7,7,7,7,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2

%N Scan primes, write down initial digit if it is a prime.

%o (PARI) firstpr(n) = { forprime(x=2,n, fd = eval(mid(Str(x),1,1)); if(isprime(fd),print1(fd",")) ) } \ Get a substring of length n from string str starting at position s in str. mid(str,s,n) = { v =""; tmp = Vec(str); ln=length(tmp); for(x=s,s+n-1, v=concat(v,tmp[x]); ); return(v) }

%Y Cf. A077648.

%K base,nonn

%O 2,1

%A _Cino Hilliard_, Apr 25 2004

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Last modified July 25 16:19 EDT 2014. Contains 244915 sequences.