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A198190 Primes from the decimal expansion of sqrt(2), sorted first by the final digit index and then by length. 0

%I

%S 41,2,421,3,13,5,2,3,23,5623,135623,42135623,4142135623,7,37,56237,3,

%T 73,373,3562373,213562373,7309,37309,5,5048801,414213562373095048801,

%U 7,887,488016887,142135623730950488016887,2,2,688724209,414213562373095048801688724209

%N Primes from the decimal expansion of sqrt(2), sorted first by the final digit index and then by length.

%e The first digit, 1, is not prime.

%e The second digit, 4, cannot terminate any prime.

%e The third digit, 1, is not prime, but 41 is, so a(1) = 41. 141 is not prime, so it is not in the sequence.

%o (PARI) v=[1, 4, 1, 4, 2, 1, 3, 5, 6, 2, 3, 7, 3, 0, 9, 5, 0, 4, 8, 8, 0, 1, 6, 8, 8, 7, 2, 4, 2, 0, 9, 6, 9]

%o for(n=1,#v,x=0;p=1;forstep(k=n,1,-1,x+=p*v[k];p*=10;if(v[k]&&isprime(x),print1(x", "))))

%Y Cf. A002193.

%K nonn,base

%O 1,1

%A _Franklin T. Adams-Watters_, Oct 21 2011

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Last modified July 5 20:21 EDT 2020. Contains 335473 sequences. (Running on oeis4.)