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 A059758 Undulating palindromic primes: numbers that are prime, palindromic in base 10, and the digits alternate: ababab... with a != b. 28
 101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929, 18181, 32323, 35353, 72727, 74747, 78787, 94949, 95959, 1212121, 1616161, 323232323, 383838383, 727272727, 919191919, 929292929, 979797979, 989898989 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES C. A. Pickover, "Wonders of Numbers", Oxford New York 2001, Chapter 52, pp. 123-124, 316-317. C. W. Trigg, Palindromic Octagonal Numbers, Journal of Recreational Mathematics, 15:1, pp. 41-46, 1982-83. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..100 P. De Geest, More undulating primes R. Ondrejka, The Top Ten: a Catalogue of Primal Configurations C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review MAPLE for l from 3 to 31 by 2 do for i from 0 to 9 do for j from 0 to 9 do it1 := sum(i*10^(2*k), k=0..(l-1)/2): it2 := sum(j*10^(2*k+1), k=0..(l-3)/2): if isprime(it1+it2) and i<>j then printf(`%d, `, it1+it2) fi: od: od: od: # James A. Sellers, Feb 13 2001 MATHEMATICA t = {}; t1 = {1, 3, 7, 9}; Do[p = 10 a + b; q = 10 b + a; t = Join[t, Select[Table[(p*10^(2 n + 1) - q)/99, {n, 4}], PrimeQ]], {a, t1}, {b, Range[0, 9]}]; Union[t] (* Jayanta Basu, Jun 23 2013 *) uppQ[n_]:=Module[{idn=IntegerDigits[n]}, OddQ[Length[idn]]&& PalindromeQ[ n] && Length[Union[Partition[idn, 2]]]==1]; Select[Prime[Range[ 51*10^6]], uppQ] (* or *) Select[FromDigits/@Flatten[Table[Riffle[Table[n, i], k], {n, {1, 3, 7, 9}}, {i, 5}, {k, 0, 9}], 2], #>9&&PrimeQ[#]&]//Sort (* The second program is significantly faster than the first. *) (* Harvey P. Dale, Feb 24 2018 *) PROG (Python) from sympy import isprime A059758_list = [] for l in range(1, 300): ....for a in '1379': ........for b in '0123456789': ............if a != b: ................p = int((a+b)*l+a) ................if isprime(p): ....................A059758_list.append(p) # Chai Wah Wu, Dec 21 2014 CROSSREFS Cf. A032758. Sequence in context: A089360 A056728 A085112 * A158089 A104946 A272075 Adjacent sequences:  A059755 A059756 A059757 * A059759 A059760 A059761 KEYWORD nonn,easy,base AUTHOR Jeff Heleen, Feb 11 2001 EXTENSIONS More terms from James A. Sellers, Feb 13 2001 STATUS approved

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Last modified December 13 22:55 EST 2019. Contains 329974 sequences. (Running on oeis4.)