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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

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Last modified April 23 22:11 EDT 2014. Contains 240947 sequences.