The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A083754 a(1) = 1 and then smallest odd number not occurring earlier such that the concatenation a(1)a(2)a(3)... is a prime. 5
 1, 3, 7, 11, 9, 27, 63, 31, 53, 21, 13, 83, 33, 39, 49, 51, 77, 87, 307, 29, 229, 281, 151, 173, 481, 41, 99, 157, 177, 17, 357, 213, 231, 171, 271, 557, 67, 113, 463, 159, 119, 57, 247, 147, 563, 409, 353, 391, 179, 1051, 209, 19, 153, 621, 287, 567, 313, 117, 363 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Conjecture: all odd numbers not of the type 10k+5 are members. Some of the larger entries may only correspond to probable primes. Values corresponding to a(6)=27 (A083755(5)) through a(59)=363 (A083755(58), a 149-digit value) have been certified prime with Primo. - Rick L. Shepherd, May 10 2003 Since we begin with 1 and thereafter have more than a single decimal digit, all terms must be in A045572, the sequence that contains all positive integers relatively prime to 10. - Michael De Vlieger, Oct 30 2020. LINKS Michael De Vlieger, Table of n, a(n) for n = 1..501 Michael De Vlieger, Plot of a(n) for 1 <= n <= 500, showing congruency of a(n) with 1 (orange), 3 (green), 7 (blue), or 9 (magenta) (mod 10). EXAMPLE 13,137,13711, etc. are primes.(1379 is not a prime) hence 11 is the next member after 7. MATHEMATICA Block[{c = 1, a = {1}, f, g}, f[m_, n_] := m*10^(1 + Floor[Log10[n]]) + n; g[n_] := (5 n + Mod[3 n + 2, 4] - 4)/2; Do[Block[{j = 2, k, d, t}, While[Nand[FreeQ[a, Set[k, g[j] ]], PrimeQ[Set[d, f[c, k]]]], j++]; c = d; AppendTo[a, k]], {i, 59}]; a] (* Michael De Vlieger, Oct 30 2020 *) PROG (PARI) {used_before(v, n) = for (l=1, matsize(v)[2], if(v[l]==n, return(1))); return(0)} {A083754=[1]; p=A083754[1]; A083755=[]; print1(A083754[1], ", "); for (m=2, 151, k=1; while (used_before(A083754, k)||!isprime(tmp_p=p*(10^length(Str(k)))+k), k=k+2); p=tmp_p; A083755=concat(A083755, p); A083754=concat(A083754, k); print1(A083754[m], ", ")); A083755} CROSSREFS Cf. A045572, A083755. Sequence in context: A260408 A261103 A262505 * A113578 A337250 A043345 Adjacent sequences: A083751 A083752 A083753 * A083755 A083756 A083757 KEYWORD base,nonn AUTHOR Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 06 2003 EXTENSIONS More terms from Rick L. Shepherd, May 08 2003 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 19 01:02 EDT 2024. Contains 376002 sequences. (Running on oeis4.)