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A217039
Primes whose decimal representation has only digits in {4,5,7}.
4
5, 7, 47, 457, 547, 557, 577, 757, 4447, 4457, 4547, 5477, 5557, 7457, 7477, 7547, 7577, 7757, 44777, 45557, 45757, 47777, 54547, 54577, 55457, 55547, 57457, 57557, 74747, 75557, 75577, 77447, 77477, 77557, 77747, 444547, 444557, 445447, 445477, 445747, 447757
OFFSET
1,1
COMMENTS
These could be called crooked primes. These are the primes in A214584. Primes whose numerals are all written (san serif) with at least one right or acute angle.
FORMULA
A000040 INTERSECTION A214584.
MATHEMATICA
Select[Flatten[Table[FromDigits/@Tuples[{4, 5, 7}, n], {n, 6}]], PrimeQ] (* Bruno Berselli, Sep 25 2012 *)
PROG
(Magma) [p: p in PrimesUpTo(450000) | Intseq(p) subset [4, 5, 7]]; // Bruno Berselli, Sep 25 2012
(PARI) A217039(n=50, show=0, L=[4, 5, 7])={for(d=1, 1e9, my(t, u=vector(d, i, 10^(d-i))~); forvec(v=vector(d, i, [if(i==d&&d>1, 3/*must end in 7*/, 1), #L]), ispseudoprime(t=vecextract(L, v)*u)||next; show&&print1(t", "); n--||return(t)))} \\ Syntax updated for newer PARI versions by M. F. Hasler, Jul 25 2015
KEYWORD
nonn,base,easy
AUTHOR
Jonathan Vos Post, Sep 24 2012
STATUS
approved