

A089987


Primes in the concatenation of consecutive numbers beginning with 2.


6




OFFSET

1,1


COMMENTS

Sum of reciprocals = 0.5434783035011462065880780409...
23, 4567 and 89 are prime numbers, thus a(3) = A262571(9) = 23456789 is a prime obtained by concatenating 3 primes that are themselves the concatenation of consecutive integers.  XU Pingya, Apr 16 2017
No other primes less than the concatenation of 2,3,4,5,6,7,8,9,10,11,12,...,9999.  Robert Price, Nov 04 2018


LINKS

Table of n, a(n) for n=1..4.


MATHEMATICA

Select[Table[FromDigits[Flatten[IntegerDigits[Range[2, n]]]], {n, 2, 30}], PrimeQ[#] & ] (* Robert Price, Nov 05 2018 *)


PROG

(PARI) concatprime(n, p) = { sr=0; y=""; for(x=p, n, y=concat(Str(y), Str(x)); z=eval(y); if(ispseudoprime(z), print1(z", "); sr+=1./z; ); ); print(); print(sr) }


CROSSREFS

Primes in A262571.
See A262300 for more information.
See also A007908 for the numbers 1234...n.
Sequence in context: A114256 A110714 A067837 * A162605 A118812 A228241
Adjacent sequences: A089984 A089985 A089986 * A089988 A089989 A089990


KEYWORD

nonn,base,more


AUTHOR

Cino Hilliard, Jan 14 2004


EXTENSIONS

Offset corrected by Michel Marcus, Apr 21 2017


STATUS

approved



