Friday, 21 February 2025

Primorial Number Base Revisited

On the 14th February 2021, now over four years ago, I created a post on this blog about the Primorial Number System. Since then, I've thought very little about it but today's number (associated with my diurnal age) reminded me once again of this number system. The number is 27718 and it is a member of OEIS A333703:


A333703   Numbers ksuch that k divides the sum of digits in primorial base of all numbers from 1 to k.


The numbers that satisfy up to 40000 are:

1, 2, 10, 22, 58, 62, 63, 64, 66, 67, 68, 118, 178, 418, 838, 1258, 1264, 1265, 1277, 1278, 1678, 2098, 4618, 9238, 10508, 10509, 10510, 10512, 10513, 10514, 13858, 14704, 14754, 18478, 23098, 23102, 23276, 27718


Table 1 shows the numbers from OEIS A333703 together with their primorial base equivalents and the progressive totals of the digits of the all the primorial numbers up and including each number. The primorial base representation I've employed here uses the base 10 digits (0 to 9) together with a space as a separator (although colons are more commonly used). However, for numbers in the range up to 40000 that I use the base 12 system using the additional digits A for 10 and B for 11 are sufficient so that concatenation of the "placeholders" does not produce any ambiguity. The primorial number then looks like a normal base 12 number which produces an ambiguity in itself.


Table 1: permalink

Table 2 shows the numbers together with their corresponding progressive totals and the results when these totals are divided by the corresponing number.


Table 2: permalink

The next number after 22718 is 60058 so I won't be around to see that. For more information see this source. I started this blog by referring to my diurnal age on the 21st February 2025 (27718) but my diurnal age on the very next day (27719) also has a property that connects it to the primorial number base.


A343048   a(n) is the least number whose sum of digits in primorial base equals n.


The members of this sequence up to 40000 are (permalink):

0, 1, 3, 5, 11, 17, 23, 29, 59, 89, 119, 149, 179, 209, 419, 629, 839, 1049, 1259, 1469, 1679, 1889, 2099, 2309, 4619, 6929, 9239, 11549, 13859, 16169, 18479, 20789, 23099, 25409, 27719, 30029

Table 3 shows the increasing values of n:


Table 3: permalink

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