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A056730 Palindromic primes with just two distinct digits. 3
101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929, 11311, 11411, 13331, 15551, 16661, 18181, 19991, 32323, 33533, 35353, 72227, 72727, 74747, 75557, 76667, 77377, 77477, 77977, 78787, 78887, 79997, 94949, 95959 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

f:= proc(d) local d1, d2, L, cand, C1, C2, C3, a, b, n, Cands;

    Cands:= NULL;

    d1:= (d+1)/2;

    d2:= d-d1;

    for b in [1, 3, 7, 9] do

      for a in {$0..9} minus {b} do

        for n from 2^(d1-1) to 2^d1-2 do

          L:= convert(n, base, 2);

          C1:= a*(10^d-1)/9;

          C2:= (b-a)*add(L[i]*10^(i+d2-1), i=1..d1);

          C3:= (b-a)*add(L[i]*10^(d1-i), i=2..d1);

          cand:= C1+C2+C3;

          if isprime(cand) then Cands:= Cands, cand; fi

    od od od;

    sort([Cands])

end proc:

map(op, [seq(f(d), d=3..7, 2)]); # Robert Israel, Sep 09 2018

MATHEMATICA

Select[ Range[ 1, 3 10^6, 2 ], PrimeQ[ # ] && Length[ Union[ RealDigits[ # ][ [ 1 ] ] ] ] == 2 && RealDigits[ # ][ [ 1 ] ] == Reverse[ RealDigits[ # ][ [ 1 ] ] ] & ]

CROSSREFS

Intersection of A002385 and A031955.

Sequence in context: A319049 A052086 A154270 * A077798 A089360 A056728

Adjacent sequences:  A056727 A056728 A056729 * A056731 A056732 A056733

KEYWORD

nonn,base

AUTHOR

Robert G. Wilson v, Aug 11 2000

STATUS

approved

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Last modified November 16 17:32 EST 2018. Contains 317275 sequences. (Running on oeis4.)