A258183 Numbers which divide the concatenation of the two surrounding primes.

7, 9, 49, 111, 1090909, 28571427, 111111111, 3333333327, 25641025641, 10576923076923, 59090909090909, 2631578947368421, 4827586206896549, 8947368421052631, 18644067796610169, 111111111111111111, 812499999999999999, 1889250814332247557, 9189189189189189189

Offset

1,1

Comments

The terms greater than 10^18 are obtained assuming that nextprime(n) < n + (log n)^2, which is known to hold at least for 4 < n < 10^18.

Links

Giovanni Resta, Table of n, a(n) for n = 1..42 (terms < 10^36)

Carlos Rivera, Puzzle 786

Example

The number 9 is in the sequence because the surrounding primes are 7 and 11 and 711 is divisible by 9.

Mathematica

Select[Range[3, 10^4], Divisible[ FromDigits[ Join@@ IntegerDigits@ NextPrime[#, {-1, 1}]], #]&]

Crossrefs

Cf. A258182, A258184.

Sequence in context: A189053 A067649 A025631 * A038275 A261669 A299913

Adjacent sequences: A258180 A258181 A258182 * A258184 A258185 A258186

Keyword

nonn,base

Author

Giovanni Resta, May 23 2015

Status

approved