A330089 a(n) is the smallest integer k such that Omega(k) = n and Omega(2*k+1) = n+1 (where Omega is A001222).

7, 22, 148, 472, 2632, 14944, 25312, 349312, 1645312, 16274560, 27565312, 163240960, 1637104000, 17758898176, 36261548032, 18847289344, 1280655450112, 5778613350400, 42629361516544, 219654008209408, 137946306445312, 4629754071040000, 53702255633760256, 9828354353004544, 404693465879805952

Offset: 1

Author

Zak Seidov, Jul 26 2020

Keywords

• nonn

Comments

Are all terms > 7 even? Is the sequence infinite?

If A115186(n + 1) is even then a(n) = A115186(n + 1) / 2. - David A. Corneth, Mar 23 2021

Examples

			n=1: 7 is prime and 2*7+1 = 15 = 3*5 is semiprime A001358(6);
n=2: 22 = 2*11 is semiprime A001358(8) and 2*22+1 = 45 = 3*3*5 is 3-almost prime A014612(10).
		

Links

• David A. Corneth, Table of n, a(n) for n = 1..27

Crossrefs

Cf. A001222, A001358, A014612, A115186.

Programs

PARI

a(n) = {my(k=1); while ((bigomega(k) != n) || (bigomega(2*k+1) != (n+1)), k++); k;} \\ Michel Marcus, Aug 20 2020

Extensions

a(14)-a(18) from Dana Jacobsen, Aug 30 2020

More terms from David A. Corneth, Mar 23 2021