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A039944 Undulating palindromic primes of form ABABAB...BA with alternating prime and nonprime digits. 3
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified September 24 16:53 EDT 2018. Contains 315347 sequences. (Running on oeis4.)