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 A056728 Palindromic primes using only two distinct digits and only the exterior digit is different. 2
 101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929, 13331, 15551, 16661, 19991, 72227, 75557, 76667, 78887, 79997, 1333331, 1444441, 1777771, 3222223, 3444443, 7666667, 9222229, 9888889 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Primes of the form a*(10^c + 1) + b*(10^c - 10)/9 for 1<=a<=9, 0<=b<=9, c >= 2, a <> b. - Robert Israel, Nov 02 2014 LINKS Robert Israel, Table of n, a(n) for n = 1..127 Patrick De Geest, PDP Reference Table. Makoto Kamada, Plateau and depression numbers of the form ABB...BBA. MAPLE f:= (a, b, n) -> a*(10^n + 1) + b*(10^n - 10)/9: select(isprime, [seq(seq(seq(f(a, b, n), b={\$0..9} minus {a}), a=1..9), n=2..8)]); # Robert Israel, Nov 02 2014 MATHEMATICA Select[Union[Flatten[Table[FromDigits[Join[{a}, PadRight[{}, n, b], {a}]], {n, 1, 7, 2}, {b, 0, 9}, {a, {1, 3, 7, 9}}]]], PrimeQ] (* Harvey P. Dale, Mar 07 2015 *) CROSSREFS Sequence in context: A056730 A077798 A089360 * A085112 A059758 A158089 Adjacent sequences:  A056725 A056726 A056727 * A056729 A056730 A056731 KEYWORD nonn,base AUTHOR Robert G. Wilson v, Aug 11 2000 EXTENSIONS Links added by Patrick De Geest, Nov 02 2014 STATUS approved

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Last modified May 15 13:20 EDT 2021. Contains 343920 sequences. (Running on oeis4.)