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A177850
Smallest n-digit emirp with only nonprime digits.
1
149, 1009, 10009, 100049, 1000849, 10000169, 100000891, 1000000009, 10000001041, 100000000669, 1000000000091, 10000000001011, 100000000000469, 1000000000004449, 10000000000001101, 100000000000000049
OFFSET
3,1
COMMENTS
Least value of emirps with only nonprime digits (i.e., 0,1,4,6,8,9) A128390, with n digits. This is to primes with nonprime digits (A034844) as smallest n-digit emirp with only prime digits (A177513) is to primes with only prime digits.
EXAMPLE
a(6) = 100049 because all digits {0,1,4,9} are nonprime, and 100049 is prime, and R(100049) = A004086(100049) = 940001 is prime, and there is no smaller 6-digit number meeting these criteria.
MAPLE
isA084984 := proc(n) convert(convert(n, base, 10), set) ; if % intersect {2, 3, 5, 7} = {} then true; else false; end if; end proc:
A177850 := proc(n) local a; a := 10^(n-1) ; while not (isA006567(a) and isA084984(a)) do a := nextprime(a) ; end do; if a < 10^n then return a ; else return -1 ; end if; end proc:
seq(A177850(n), n=3..40) ; # R. J. Mathar, May 24 2010
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Jonathan Vos Post, May 14 2010
EXTENSIONS
More terms from R. J. Mathar, May 24 2010
STATUS
approved