A124050 Difference between (first Chen prime > 10^n) and 10^n.

1, 1, 1, 9, 7, 19, 37, 19, 7, 7, 19, 19, 61, 687, 97, 91, 79, 13, 79, 97, 151, 217, 427, 253, 667, 13, 127, 427, 457, 577, 1069, 349, 1147, 1267, 2527, 2833, 709, 871, 259, 361, 1651, 391, 2689, 649, 31, 3007, 1657, 2257, 3757, 5977, 1441, 2779, 5749, 367, 31

Offset

0,4

Comments

A033873(n) <= a(n) <= A124001(n) and a(n) = A033873(n) for n = 0, 1, 2, 3, 4, 7, 8, 9, 10, 25, 44, 54.

Links

Table of n, a(n) for n=0..54.

Example

a(0) = 1 because 2 is prime, 2 + 2 = 4 semiprime and 2 - 10^0 = 1,
a(1) = 1 because 11 and 13 are twin primes and 11 - 10^1 = 1,
a(2) = 1 because 101 and 103 are twin primes and 101 - 10^2 = 1,
a(3) = 9 because 1009 is prime, 1011 = 3*337 semiprime and 1009 - 10^3 = 9,
a(4) = 7 because 10007 and 10009 are twin primes and 10007 - 10^4 = 7,
a(5) = 19 because 100019 is prime, 100021 = 29*3449 semiprime and 100019 - 10^5 = 19, etc.

Crossrefs

Cf. A033873, A109611, A124001.

Sequence in context: A131724 A190995 A186830 * A107663 A298780 A231605

Adjacent sequences: A124047 A124048 A124049 * A124051 A124052 A124053

Keyword

nonn

Author

Zak Seidov, Nov 03 2006

Status

approved