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A117801 Triangular numbers for which the product of the digits is a prime number. +0
1
3, 15, 21, 171, 1711 (list; graph; listen)
OFFSET

1,1

COMMENT

None of the digits can be 0,4,6,8 or 9. All the digits must be 1 or, just one digit can be 2,3,5 or 7 and all the others are 1.

There are no more terms less than 10^2580. - Hans Havermann (pxp(AT)rogers.com), May 07 2006

EXAMPLE

1711 is in the sequence because (1)it is a triangular number and (2)the product of its digits is 1*7*1*1=7, which is a prime number.

CROSSREFS

Cf. A000217.

Sequence in context: A014493 A076825 A118565 this_sequence A087674 A009057 A083795

Adjacent sequences: A117798 A117799 A117800 this_sequence A117802 A117803 A117804

KEYWORD

more,nonn,base

AUTHOR

Luc Stevens (lms022(AT)yahoo.com), Apr 29 2006

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Last modified August 29 17:54 EDT 2008. Contains 143238 sequences.


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