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URL: https://oeis.org/A390601

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A390601
Positive integers (not multiples of 10) whose (radix-10) constant congruence speed is greater than the minimum of the (radix-10) constant congruence speeds of all their prime factors.
1
15, 18, 24, 25, 26, 32, 45, 51, 55, 57, 65, 68, 74, 75, 76, 82, 85, 93, 95, 99, 105, 115, 118, 124, 126, 132, 135, 143, 145, 155, 165, 168, 174, 175, 176, 182, 185, 195, 201, 205, 207, 215, 218, 224, 225, 226, 232, 235, 243, 249, 255, 265, 268, 274, 275, 276
OFFSET
1,1
COMMENTS
Consider the radix-10 numeral system. For the definition of "constant congruence speed", see A373387 (see also the comments to A391434).
In general, if the product of two positive integers r and s is not divisible by 10, then the constant congruence speed of r*s is necessarily >= the minimum of the constant congruence speeds of r and s: the present sequence arises from the > case.
By definition, this sequence contains no primes (since the constant congruence speed of any prime equals that of its unique prime divisor).
EXAMPLE
a(1) = 15 since the constant congruence speed of 3 is 1, the constant congruence speed of 5 is 2, the constant congruence speed of 15 is 4, and 4 > min{1,2}.
KEYWORD
nonn,base
AUTHOR
STATUS
approved