A145443 In class n of the phi iteration, the number of primes less than the smallest composite number.

1, 2, 2, 2, 2, 1, 3, 1, 1, 2, 0, 0, 0, 1, 0, 1, 3, 0, 1, 0, 1, 1, 0, 0, 1, 1, 0, 0, 4, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 2, 2, 1, 0, 1, 0, 2, 0, 0, 1, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 2, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset

1,2

Comments

A number is in class n if n iterations of Euler's phi function produces 2 (see A032358). a(n)>0 for the n in A136040.

Links

T. D. Noe, Table of n, a(n) for n=1..1000

T. D. Noe, Computing Numbers in Section I of the Totient Iteration

Example

According to A005239, class 5 begins with 41, 47, 51, 53, 55, 59, 61. There are two primes less than the composite 51. Hence a(5)=2.

Crossrefs

A098196

Sequence in context: A054715 A254668 A306250 * A192056 A207385 A306242

Adjacent sequences: A145440 A145441 A145442 * A145444 A145445 A145446

Keyword

nonn

Author

T. D. Noe, Oct 10 2008

Extensions

Modified comment. - T. D. Noe, Nov 18 2008

Extension T. D. Noe, Nov 18 2008

Status

approved