OFFSET
1,1
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.
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
EXAMPLE
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.
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
CROSSREFS
KEYWORD
base,easy,fini,full,nonn
AUTHOR
Jonathan Vos Post, May 27 2007
STATUS
approved