

A071119


Palindromic primes in which deleting the outside pair of digits yields a prime at every stage until finally a singledigit prime is obtained.


2



2, 3, 5, 7, 131, 151, 353, 373, 727, 757, 929, 11311, 31513, 33533, 37273, 37573, 39293, 71317, 93739, 97579, 1335331, 3315133, 3392933, 7392937, 9375739, 373929373, 733929337
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OFFSET

1,1


REFERENCES

J.P. Delahaye, "Pour la science", (French edition of Scientific American), Juin 2002, p. 99.
G. L. Honaker, Jr. and C. Caldwell, Palindromic prime pyramids, J. Recreational Mathematics, vol. 30.3, pp. 169176, 19992000.


LINKS

Table of n, a(n) for n=1..27.
G. L. Honaker, Jr. and C. K. Caldwell, Palindromic Prime Pyramids
G. L. Honaker, Jr. and C. K. Caldwell, Supplement to "Palindromic Prime Pyramids"
I. Peterson, MathTrek, Primes, Palindromes and Pyramids


EXAMPLE

31513 is in the sequence because 31513, 151 and 5 are primes.
a(17) = 39293 because 39293, 929 and 2 are primes.


PROG

(PARI) V = [2, 3, 5, 7]; vCount = 4; x = [1, 3, 7, 9]; print(V); forstep (i = 2, 20, 2, newV = vector(4*vCount); newCount = 0; for (j = 1, 4, for (k = 1, vCount, n = x[j]*(10^i + 1) + 10*V[k]; if (isprime(n), print(n); newCount = newCount + 1; newV[newCount] = n))); V = newV; vCount = newCount) \\ David Wasserman, Oct 04 2004


CROSSREFS

Cf. A002385.
Sequence in context: A039944 A076611 A082805 * A157869 A046705 A054218
Adjacent sequences: A071116 A071117 A071118 * A071120 A071121 A071122


KEYWORD

base,easy,fini,full,nonn


AUTHOR

Lior Manor May 28 2002


EXTENSIONS

Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 14 2007


STATUS

approved



