A039944 Undulating palindromic primes of form ABABAB...BA with alternating prime and nonprime digits.

2, 3, 5, 7, 131, 151, 313, 383, 787, 797, 929, 74747, 78787, 95959, 1212121, 383838383, 929292929, 979797979, 12121212121, 151515151515151, 383838383838383, 38383838383838383, 74747474747474747, 95959595959595959, 383838383838383838383, 787878787878787878787

Offset: 1

Author

G. L. Honaker, Jr.

Keywords

• base
• nonn

Comments

There are 52 terms of integer length 999 or less. The first term with integer length greater than 999 has 1295 digits and is 9595...5959. - Harvey P. Dale, Jul 12 2018

References

• C. A. Pickover, "Wonders of Numbers", Oxford New York 2001, Chapter 52, pp. 123-124, 316-317.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..52
• C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review

Programs

Mathematica

f[x_]:=Module[{pr,cm},pr=Select[Flatten[Table[FromDigits[PadRight[{},x,{a,b}]],{a,{3,7}},{b,{1,4,6,8,9}}]],PrimeQ];cm=Select[ Flatten[ Table[ FromDigits[PadRight[{},x,{a,b}]],{a,{1,9}},{b,{2,3,5,7}}]],PrimeQ]; Sort[ Join[pr,cm]]]; Join[{2,3,5,7},Flatten[ Table[ f[x],{x,3,999,2}]]]//Union (* Harvey P. Dale, Jul 12 2018 *)

Extensions

More terms from Harvey P. Dale, Jul 12 2018