A117801 Triangular numbers for which the product of the digits is a prime number.

3, 15, 21, 171, 1711

Offset

1,1

Comments

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, May 07 2006

Links

Table of n, a(n) for n=1..5.

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.

Mathematica

Select[Accumulate[Range[100000]], PrimeQ[Times@@IntegerDigits[#]]&] (* _Harvey Dale_, Dec 04 2010 *)
Select[Table[n(n + 1)/2, {n, 10^3}], PrimeQ[Times@@IntegerDigits[#]]&] (* Zak Seidov, Dec 04 2010 *)

Prog

(PARI) isok(t) = ispolygonal(t, 3) && isprime(vecprod(digits(t))); \\ Michel Marcus, Jul 16 2022

Crossrefs

Cf. A000217.

Sequence in context: A259745 A118565 A230658 * A347303 A277585 A318134

Adjacent sequences: A117798 A117799 A117800 * A117802 A117803 A117804

Keyword

more,nonn,base

Author

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

Status

approved