A114314 Difference between the first odd semiprime > 7^n and 7^n.

8, 2, 2, 12, 6, 10, 2, 6, 12, 2, 4, 12, 2, 10, 2, 4, 10, 6, 4, 4, 12, 24, 10, 10, 10, 4, 2, 30, 10, 4, 4, 30, 12, 2, 10, 4, 10, 10, 54, 10, 12, 22, 10, 24, 2, 4, 88, 16, 16, 22, 30, 6, 60, 12, 2, 8, 22, 30, 10, 10, 88, 6, 34, 6, 22, 22, 94, 40, 6, 30, 4, 100, 40, 16, 40, 4, 36, 20, 4, 16, 18

Offset: 0

Author

Jonathan Vos Post, Feb 05 2006

Keywords

• easy
• nonn

Comments

A098147 is the difference between the first odd semiprime > 10^n and 10^n.

Examples

			a(0) = 8 because 7^0 + 8 = 9 = 3^2 is an odd semiprime.
a(1) = 2 because 7^1 + 2 = 9 = 3^2 is an odd semiprime.
a(2) = 2 because 7^2 + 2 = 51 = 3*17 is an odd semiprime.
a(3) = 12 because 7^3 + 12 = 355 = 5 * 71.
a(4) = 6 because 7^4 + 6 = 2407 = 29 * 83 (brilliant).
a(5) = 10 because 7^5 + 10 = 16817 = 67 * 251.
		

Crossrefs

Cf. A000351, A001358, A098147.

Formula

a(n) = minimum integer k such that 7^n + k is an element of A046315. a(n) = minimum integer k such that A000420(n) + k is an element of A046315.

Extensions

Corrected and extended by Don Reble, Oct 16 2017