login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A108638 Semiprime plus its digits is semiprime. 0
15, 22, 26, 33, 38, 39, 49, 51, 55, 57, 74, 77, 115, 123, 129, 134, 145, 155, 161, 169, 178, 187, 202, 206, 213, 214, 221, 237, 254, 265, 274, 278, 291, 299, 301, 303, 309, 321, 327, 335, 361, 371, 377, 381, 382, 386, 411, 437, 445, 466, 478, 485, 497, 505 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Surprisingly there are only three(?) semiprimes sp, 10,14,15, such that sp minus its digits is semiprime.

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

15=3*5 and 15+1+5=21=3*7.

MATHEMATICA

Select[Range[500], Plus@@Last/@FactorInteger[ # ]==Plus@@Last/@FactorInteger[ #+Plus@@IntegerDigits[ # ]]==2&]

CROSSREFS

Sequence in context: A018888 A115174 A092783 * A076379 A227095 A038753

Adjacent sequences:  A108635 A108636 A108637 * A108639 A108640 A108641

KEYWORD

nonn,base

AUTHOR

Zak Seidov, Jun 14 2005

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified December 19 08:21 EST 2014. Contains 252186 sequences.