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 A140748 a(n) is the number of divisors of n that are not coprime to the next larger divisor of n. 2
 0, 0, 0, 1, 0, 1, 0, 2, 1, 1, 0, 2, 0, 1, 1, 3, 0, 3, 0, 3, 1, 1, 0, 4, 1, 1, 2, 3, 0, 3, 0, 4, 1, 1, 1, 5, 0, 1, 1, 4, 0, 4, 0, 3, 2, 1, 0, 6, 1, 3, 1, 3, 0, 5, 1, 4, 1, 1, 0, 6, 0, 1, 2, 5, 1, 4, 0, 3, 1, 3, 0, 7, 0, 1, 3, 3, 1, 4, 0, 6, 3, 1, 0, 6, 1, 1, 1, 5, 0, 6, 1, 3, 1, 1, 1, 8, 0, 3, 3, 6, 0, 4, 0, 5, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,8 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 FORMULA A140747(n) + a(n) = A000005(n) - 1. EXAMPLE The divisors of 20 are 1,2,4,5,10,20. 1 is coprime to 2. 2 is not coprime to 4. 4 is coprime to 5. 5 is not coprime to 10. And 10 is not coprime to 20. So there are 3 divisors, 2, 5 and 10, that are each not coprime to the next higher divisor. So a(20) = 3. PROG (PARI) A140748(n) = { my(s=0, pd=0); fordiv(n, d, s += (pd&&(1

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Last modified June 12 10:58 EDT 2021. Contains 344947 sequences. (Running on oeis4.)