A083439 a(1) = 3; then a(n+1) = smallest prime not already in the sequence such that the concatenations a(n)a(n+1) and a(n+1)a(n) are both primes.

3, 7, 19, 13, 61, 151, 31, 139, 67, 37, 79, 193, 163, 127, 157, 97, 43, 103, 307, 367, 457, 643, 73, 277, 223, 229, 373, 199, 109, 313, 211, 271, 241, 421, 181, 283, 397, 337, 349, 331, 577, 523, 463, 613, 439, 541, 571, 433, 787, 547, 661, 769, 487, 601, 823, 709

Offset

3,1

Links

Table of n, a(n) for n=3..58.

Prog

(PARI) { p=3; S=Set(); while(!setsearch(S, p), S=setunion(S, Set([p])); print1(p, ", "); forprime(q=2, 10^4, if(setsearch(S, q), next); if( isprime(eval(concat(Str(p), Str(q)))) && isprime(eval(concat(Str(q), Str(p)))), p=q; break))) } \\ Max Alekseyev, Apr 24 2009

Crossrefs

Cf. A073641, A075609.

Sequence in context: A217371 A088629 A075609 * A151858 A365139 A242170

Adjacent sequences: A083436 A083437 A083438 * A083440 A083441 A083442

Keyword

base,nonn

Author

Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Apr 30 2003

Extensions

Corrected and extended by Max Alekseyev, Apr 24 2009

Status

approved