A071119 Palindromic primes in which deleting the outside pair of digits yields a prime at every stage until finally a single-digit prime is obtained.

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

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. 169-176, 1999-2000.

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