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

1,1

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

Links

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

Example

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).

Prog

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

Crossrefs

Cf. A001222, A001358, A014612, A115186.

Sequence in context: A117110 A027838 A194996 * A000835 A239028 A335638

Adjacent sequences: A330086 A330087 A330088 * A330090 A330091 A330092

Keyword

nonn

Author

Zak Seidov, Jul 26 2020

Extensions

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

More terms from David A. Corneth, Mar 23 2021

Status

approved