A123933 a(n) = smallest positive composite integer such that a(n)-10^k is prime for all k=1,2..n.

12, 111, 1007, 10109, 100709, 1008819, 10326309, 106635053, 1006357961, 10413717671, 100795008839

Offset

1,1

Links

Table of n, a(n) for n=1..11.

Formula

a(n) == 0 (mod 7) for n > 6.

Example

a(3) = 1007 as 997, 907 and 7 are primes.

Prog

(PARI) a(n) = {m = 10^n; ok = 0; while (! ok, if (! isprime(m), ok = 1; for (k=1, n, if (! isprime(m-10^k), ok = 0; break; ); ); ); if (! ok, m++); ); return (m); } \\ Michel Marcus, Jul 16 2013

Crossrefs

Sequence in context: A153597 A036733 A253091 * A199691 A348150 A077754

Adjacent sequences: A123930 A123931 A123932 * A123934 A123935 A123936

Keyword

nonn,hard,more

Author

Anton Vrba (antonvrba(AT)yahoo.com), Nov 29 2006

Extensions

a(9)-a(10) from Michel Marcus, Jul 16 2013

a(11) from Amiram Eldar, Jul 22 2025

Status

approved