

A343827


Numbers which are the product of two Sprimes (A057948) in exactly two ways.


4



441, 693, 1089, 1197, 1449, 1617, 1881, 1953, 2277, 2541, 2709, 2793, 2961, 3069, 3249, 3381, 3717, 3933, 4221, 4257, 4473, 4557, 4653, 4761, 4977, 5229, 5301, 5841, 5929, 6321, 6417, 6489, 6633, 6741, 6897, 6909, 7029, 7353, 7581, 7821, 8001, 8037, 8217, 8253
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OFFSET

1,1


COMMENTS

First differs from A057950 at a(21)=4473, whereas A057950(21)=4389, which can be represented as the product of two Sprimes in exactly 3 ways.
There exist numbers which are the product of two Sprimes in exactly 1, 2, and 3 ways; however, it is unknown if any numbers exist which are the product of two Sprimes in exactly 4 ways.


LINKS



FORMULA



EXAMPLE

1449=9*161=21*69 which are all Sprimes (A057948), and admits no other Sprime factorizations.


PROG

isok(n) = sumdiv(n, d, (d<=n/d) && is(d) && is(n/d)) == 2; \\ Michel Marcus, May 01 2021


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



