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

Author

Giovanni Resta, May 23 2015

Keywords

• nonn
• base

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.

Examples

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

Links

• Giovanni Resta, Table of n, a(n) for n = 1..42 (terms < 10^36)
• Carlos Rivera, Puzzle 786

Crossrefs

Cf. A258182, A258184.

Programs

Mathematica

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