A069604 a(1) = 1; for n>1, a(n) = smallest number with all odd digits giving a prime in concatenation with the previous terms.

1, 1, 3, 11, 1, 3, 3, 53, 13, 39, 9, 3, 399, 11, 9, 133, 3, 11, 51, 111, 13, 53, 31, 3, 173, 1, 317, 519, 579, 1, 573, 357, 5111, 39, 51, 73, 3317, 1977, 5173, 579, 357, 359, 9, 57, 3991, 959, 951, 7, 111, 1959, 39, 191, 3357, 3151, 3137, 577, 117, 1353, 951, 153, 99

Offset: 1

Author

Amarnath Murthy, Mar 26 2002

Keywords

• nonn
• base

Examples

			a(5) = 1 and the number 113111 is a prime.
		

Crossrefs

Cf. A033680, A074336, A092528, A069602.

Programs

Mathematica

a[1] = 1; a[n_] := a[n] = Block[{k = 1, c = IntegerDigits @ Table[ a[i], {i, n - 1}]}, While[ Union[ Mod[ IntegerDigits[k], 2]] != {1} || !PrimeQ[ FromDigits[ Join[ Flatten[c], IntegerDigits[k]]]], k = k + 1]; k]; Table[ a[n], {n, 61}] (* corrected by Jason Yuen, Jun 22 2025 *)

Extensions

Corrected and extended by Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Mar 30 2003