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A337230 Numbers that are a divisor of the product of the digits of its divisors. 2
1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 14, 15, 16, 18, 21, 24, 25, 27, 28, 32, 35, 36, 42, 45, 48, 54, 56, 63, 64, 72, 75, 84, 96, 112, 125, 126, 128, 135, 144, 147, 162, 168, 175, 189, 192, 224, 225, 252, 256, 288, 294, 336, 375, 378, 384, 441, 448, 486, 512, 567, 576, 588, 625, 672, 675, 729 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

In the first 130 million numbers there are 117 terms, the last being 234375. It is possible no more terms exist, although this is unknown.

The number with the largest ratio of it divisors' digit product to the number itself is 5376, with a ratio of ~2.2*10^43.

From David A. Corneth, Aug 22 2020: (Start)

The product of the digits of divisors must be nonzero. For example, 10 isn't a term as the product of digits of divisors is 0.

Terms are 7-smooth.

The largest term is 234375. Proof:

2^k1 has a 0 for k1 = 10, 3^k2 has a 0 for k2 = 10, 5^k3 has a 0 for k3 = 8 and 7^k4 has a 0 for k4 = 4.

Checking all numbers of the form 2^e1 * 3^e2 * 5^e3 * 7^e4 with ei bounded by the respective ki gives the 117 terms mentioned above with the largest of them being 234375. (End)

LINKS

Scott R. Shannon, Table of n, a(n) for n = 1..117

EXAMPLE

a(4) = 4 is a term as the divisors of 4 are 1,2,4 and 1*2*4 = 8 which is a divisible by 4.

a(10) = 12 is a term as the divisors of 12 are 1,2,3,4,6,12 and 1*2*3*4*6*1*2 = 288 which is divisible by 12.

a(19) = 28 is a term as the divisors of 28 are 1,2,4,7,14,28 and 1*2*4*7*1*4*2*8 = 3584 which is divisible by 28.

MATHEMATICA

Select[Range[3^6], (prod = Times @@ (Times @@@ IntegerDigits @ Divisors[#])) > 0 && Divisible[prod, #] &] (* Amiram Eldar, Aug 22 2020 *)

PROG

(PARI) is(n) = {if(n < 10, return(n > 0)); f = factor(n); if(f[#f~, 1] > 7, return(0)); my(d = divisors(n), p = 1); for(i = 2, #d, dd = digits(d[i]); for(j = 1, #dd, p *= dd[j]); if(p == 0, return(0))); p % n == 0} \\ David A. Corneth, Aug 22 2020

CROSSREFS

Cf. A002473, A027750, A000005, A007954, A007602, A005349, A038186, A333617.

Sequence in context: A290387 A342950 A238985 * A226900 A111228 A324022

Adjacent sequences:  A337227 A337228 A337229 * A337231 A337232 A337233

KEYWORD

nonn,fini,full,base

AUTHOR

Scott R. Shannon, Aug 20 2020

STATUS

approved

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Last modified January 20 10:18 EST 2022. Contains 350471 sequences. (Running on oeis4.)