cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A333960 Numbers k with digits in nondecreasing order and each digit > 1 such that the iterated product of digits of k is a prime and k is the least positive integer with this property and its product of digits.

Original entry on oeis.org

2, 3, 5, 7, 26, 35, 37, 57, 355, 278, 279, 359, 299, 557, 389, 579, 999, 2699, 2799, 5579, 5777, 3889, 4788, 3999, 35559, 26999, 29999, 47888, 277777, 357799, 267999, 557779, 288999, 2777778, 689999, 779999, 2688888, 7777888, 26777777, 6788899, 27777899, 47778899, 67788888, 77788888, 2677777889, 7777777788, 26888888889
Offset: 1

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Author

David A. Corneth, Apr 11 2020

Keywords

Comments

Primitive sequence to A333955.

Examples

			26 is in the sequence. It has iterated product of digits 2 which is prime and its digits are in nondecreasing order and all digits are > 1 and 26 is the least integer with these properties having product of digits 12.
34 is not in the sequence. It has all properties mentioned above except it has product of digits 12 where 34 isn't the least positive integer with those properties and product of digits 12.
		

Crossrefs

A385727 Minimum base in which the least number with absolute multiplicative persistence n achieves such persistence.

Original entry on oeis.org

0, 2, 3, 6, 9, 13, 17, 23, 26, 29, 41, 53, 53, 73, 123, 159, 157, 251, 332, 491, 587, 691, 943, 1187, 1187, 1804, 2923, 2348, 6241, 3541, 3541, 7082, 7082, 14164, 10623, 14164, 28328, 56656, 98533
Offset: 0

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Author

Brendan Gimby, Jul 08 2025

Keywords

Comments

a(n) is the minimum base in which the n-th term in A330152 achieves its absolute persistence.

Examples

			23 when represented in base 6 goes 35 -> 23 -> 10 -> 1, has absolute persistence of 3, and has smaller persistence in all smaller bases, so a(3) = 6 (Cf. A064867).
52 when represented in base 9 goes 57 -> 38 -> 26 -> 13 -> 3, has absolute persistence of 4, and has smaller persistence in all smaller bases, so a(4) = 9 (Cf. A064868).
		

Crossrefs

Programs

  • Python
    from math import prod
    from sympy.ntheory.digits import digits
    def mp(n, b): # multiplicative persistence of n in base b [from Michael S. Branicky in A330152]
        c = 0
        while n >= b:
            n, c = prod(digits(n, b)[1:]), c+1
        return c
    def a(n):
        k = 0
        while True:
            if b := next((b for b in range(2, max(3, k)) if mp(k, b)==n), 0): return b
            k += 1
    print([a(n) for n in range(11)])

Extensions

a(36)-a(38) from Jinyuan Wang, Jul 13 2025
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