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A129336 Digital clock semiprimes. 3
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 (list; graph; refs; listen; history; text; internal format)
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

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

Sequence in context: A176540 A108764 A193801 * A226526 A103607 A264815

Adjacent sequences:  A129333 A129334 A129335 * A129337 A129338 A129339

KEYWORD

base,easy,fini,full,nonn

AUTHOR

Jonathan Vos Post, May 27 2007

STATUS

approved

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Last modified August 26 03:38 EDT 2019. Contains 326324 sequences. (Running on oeis4.)