A039944 - OEIS

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

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OFFSET

1,1

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

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 *)

CROSSREFS

Sequence in context: A090718 A167853 A117703 * A076611 A082805 A071119

Adjacent sequences: A039941 A039942 A039943 * A039945 A039946 A039947

KEYWORD

base,nonn

AUTHOR

G. L. Honaker, Jr.

EXTENSIONS

More terms from Harvey P. Dale, Jul 12 2018

STATUS

approved