A129336 Digital clock semiprimes.

4, 6, 9, 10, 14, 15, 21, 22, 25, 26, 33, 34, 35, 38, 39, 46, 49, 51, 55, 57, 58, 106, 111, 115, 118, 119, 121, 122, 123, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 201, 202, 203, 205, 206, 209, 213, 214, 215, 217, 218, 219, 221, 226, 235, 237, 247

Offset: 1

Author

Jonathan Vos Post, May 27 2007

Keywords

• base
• easy
• fini
• full
• nonn

Comments

Semiprime analog of A050246. Semiprimes possible on a 24-hour digital clock, with no seconds. The largest value is a(414) = 2359 = 7 * 337 because 23:59 is the largest 4-digit number that appears on a 24-hour digital clock.

Examples

			253 is in the sequence because (see the comic) a character looks at a digital clock reading 2:53 and says: "253 is 11 x 23." That clock-time is a semiprime.
		

Links

• Nathaniel Johnston, Table of n, a(n) for n = 1..414 (full sequence)
• Randall Munroe, Factoring the Time
• Eric Weisstein's World of Mathematics, Clock Prime

Crossrefs

Cf. A001358, A050246, A118848, A118849, A118850.

Programs

Maple

with(numtheory): for h from 0 to 23 do for m from 0 to 59 do t:=100*h+m: if(bigomega(t)=2)then printf("%d, ",t): fi: od: od: # Nathaniel Johnston, May 17 2011