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A153431 a(n) is the smallest number m such that all n+1 numbers m*10^k+1 k=0,1, ...,n are prime. 2
1, 1, 1, 4, 28, 28, 170926, 170926, 931371868, 15538734736, 89468493268, 6009549731752, 89984938946056, 43000687652274618 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,4
COMMENTS
If n<m and r=10^n*a(m)*a(n)-1 is prime then r has at least n+1
representations of the form p*q-(p+q)where p & q are prime.
For n>3, 7 divides a(n). a(10) is greater than 4*10^10.
LINKS
Prime Puzzles Two Bergot questions
EXAMPLE
28+1, 280+1, 2800+1, 28000+1, 280000+1 & 2800000+1 are prime and 28 is the smallest such number so a(5)=28.
CROSSREFS
Cf. A153432.
Sequence in context: A038706 A358863 A222594 * A043074 A137314 A032405
KEYWORD
nonn,more
AUTHOR
Farideh Firoozbakht, Mar 15 2009, Mar 27 2009
EXTENSIONS
a(11)-a(13) from Don Reble, Jul 06 2022
STATUS
approved

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Last modified March 29 05:16 EDT 2024. Contains 371264 sequences. (Running on oeis4.)