A069833 Prefixing, suffixing or inserting a 9 in the number anywhere gives a prime.

7, 19, 37, 41, 91, 199, 209, 239, 311, 539, 587, 661, 749, 923, 931, 941, 967, 1009, 1079, 1139, 1997, 2717, 2959, 3971, 3979, 4559, 4993, 4999, 5393, 5629, 5651, 6401, 6739, 6911, 8213, 8491, 8939, 9109, 9397, 9607, 9679, 9829, 11089, 11227, 13943

Offset

1,1

Links

Giovanni Resta, Table of n, a(n) for n = 1..2128 (terms < 10^13, first 1175 terms from Chai Wah Wu)

Prog

(PARI) is(n, L=logint(n+!n, 10)+1, d, P)={!for(k=0, L, isprime((d=divrem(n, P=10^(L-k)))[2]+(10*d[1]+9)*P)||return)} \\ M. F. Hasler, May 10 2018

Crossrefs

Cf. A215421 (subsequence of primes).

Cf. A068679 (1 is prefixed, appended or inserted anywhere), A069246 (primes among these), A068673 (1 is prefixed, or appended).

Cf. A158594 (3 is prefixed, appended or inserted anywhere), A215419 (primes among these).

Cf. A069832 (7 is prefixed, appended or inserted anywhere), A215420 (primes among these), A068677 (7 is prefixed or appended).

Cf. A158232 (13 is prefixed or appended).

Cf. A164329 (0 is inserted), A216169 (subset of composite terms), A215417 (subset of primes), A159236 (0 is inserted between all digits).

Sequence in context: A124270 A298565 A068678 * A215421 A192594 A352243

Adjacent sequences: A069830 A069831 A069832 * A069834 A069835 A069836

Keyword

nonn,base

Author

Amarnath Murthy, Apr 14 2002

Extensions

More terms from Vladeta Jovovic, Apr 16 2002

Corrected offset by Chai Wah Wu, Oct 10 2019

Status

approved