A305900 Filter sequence for a(primes > 3) = constant sequences.

1, 2, 3, 4, 5, 6, 5, 7, 8, 9, 5, 10, 5, 11, 12, 13, 5, 14, 5, 15, 16, 17, 5, 18, 19, 20, 21, 22, 5, 23, 5, 24, 25, 26, 27, 28, 5, 29, 30, 31, 5, 32, 5, 33, 34, 35, 5, 36, 37, 38, 39, 40, 5, 41, 42, 43, 44, 45, 5, 46, 5, 47, 48, 49, 50, 51, 5, 52, 53, 54, 5, 55, 5, 56, 57, 58, 59, 60, 5, 61, 62, 63, 5, 64, 65, 66, 67, 68, 5, 69, 70, 71, 72, 73, 74, 75, 5, 76

Offset: 1

Author

Antti Karttunen, Jun 14 2018

Keywords

• nonn

Comments

For all i, j:

a(i) = a(j) => A305801(i) = A305801(j) => A305800(i) = A305800(j).

a(i) = a(j) => A007949(i) = A007949(j).

a(i) = a(j) => A305893(i) = A305893(j).

Links

• Antti Karttunen, Table of n, a(n) for n = 1..100000

Crossrefs

Cf. A305800, A305801, A305893.

Cf. also A305901, A305902, A305903 (this filter applied to various permutations of N).

Programs

PARI

A305900(n) = if(n<=5,n,if(isprime(n),5,3+n-primepi(n)));

Formula

For n <= 5, a(n) = n, for >= 5, a(n) = 5 when n is a prime, and a(n) = 3+n-A000720(n) when n is a composite.