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A089987 Primes in the concatenation of consecutive numbers beginning with 2. 6
2, 23, 23456789, 23456789101112131415161718192021222324252627 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 20 20:12 EDT 2019. Contains 327247 sequences. (Running on oeis4.)