A088604 -id:A088604 - cp's OEIS frontend

A088603 a(n) = smallest prime in which n substrings containing the most significant digit are primes.

2, 23, 233, 2333, 23333, 233993, 2339933, 23399339, 1979339333, 23339531339, 293999994791, 3733799959397, 233323747999733, 2333939994739931, 23833939369399333, 238339393693993337, 23833939369399333613

Offset: 1

Amarnath Murthy, Oct 15 2003

Agrees with A127889 for 8 terms, but A127889 ends there while this sequence continues. - Ray Chandler, Mar 13 2007

Cf. A088604, A127889.

f(n, d, spare) = local(p, r); if (!d, return(n)); for (i = 0, 9, p = 10*n + i; if (isprime(p) || spare, r = f(p, d - 1, spare - 1 + isprime(p))); if (r, return(r))); 0;
a(n) = local(i, r); i = 0; while (1, r = f(0, n + i, i); if (r, return(r), i++)); \\ David Wasserman, Aug 12 2005

Corrected and extended by David Wasserman, Aug 12 2005

A127891 Smallest n-digit left-truncatable prime.

Original entry on oeis.org

2, 13, 113, 1223, 12113, 121283, 1237547, 12184967, 124536947, 1219861613, 12181833347, 121339693967, 1213536676883, 12673876537547, 121848768729173, 1275463876537547, 12429121339693967, 165678739293946997, 1276812967623946997, 15396334245663786197, 315396334245663786197, 5918918997653319693967, 57686312646216567629137, 357686312646216567629137

Offset: 1

Ray Chandler, Feb 04 2007

Ends at a(24) = 357686312646216567629137.

Agrees with A088604 for 24 terms, but this sequence ends there while A088604 continues.

Ray Chandler, Table of n, a(n) for n = 1..24
I. O. Angell and H. J. Godwin, On Truncatable Primes, Math. Comput. 31, 265-267, 1977.
Index entries for sequences related to truncatable primes

Cf. A024785, A050987, A088604, A127892.

grow[p_, digits_] := Select[ Table[ FromDigits[Join[{k}, IntegerDigits[p]]], {k, 1, 9}], PrimeQ[#] && Length[ IntegerDigits[#]] == digits&]; g[1] = {3, 7}; g[n_] := g[n] = grow[#, n]& /@ g[n-1] // Flatten; a[1] = 2; a[n_] := Min[g[n]]; Table[a[n], {n, 1, 24}] (* Jean-François Alcover, Aug 05 2013 *)

cp's OEIS Frontend

A088603 a(n) = smallest prime in which n substrings containing the most significant digit are primes.

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