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A283561
Concatenation of the first a(n) nonsquares gives a prime.
1
1, 2, 5, 550, 832
OFFSET
1,2
COMMENTS
Indices n for which A283560(n) is prime.
A283560(1) = 2, A283560(2) = 23, A283560(5) = 23567, A283560(550) = 23567810...570571572573 is 1554-digits prime, A283560(832) = 23567810...858859860861 is 2400-digits prime.
Next term, if there is, will be more than 6100.
LINKS
Eric Weisstein's World of Mathematics, Consecutive Number Sequences
MATHEMATICA
cns[n_]:=FromDigits[Flatten[IntegerDigits[Table[k+Floor[1/2+Sqrt[k]], {k, 1, n}]]]]
Select[Table[cns[n], {n, 6100}], PrimeQ]
PROG
(PARI) is(n)=my(s=""); for(k=1, n, s=Str(s, (sqrtint(4*k)+1)\2 + k)); ispseudoprime(eval(s)) \\ Charles R Greathouse IV, Mar 10 2017
CROSSREFS
KEYWORD
base,nonn,more
AUTHOR
XU Pingya, Mar 10 2017
STATUS
approved