A124270 Prime(3almostprime(n))-3almostprime(prime(n)). Commutator [A000040,A014612] at n.

7, 19, 34, 41, 53, 44, 38, 103, 91, 73, 99, 75, 135, 142, 147, 118, 133, 125, 118, 193, 229, 191, 212, 202, 197, 201, 216, 213, 248, 239, 209, 248, 279, 279, 277, 277, 333, 325, 350, 327, 299, 308, 264, 309, 314, 322, 297, 281, 363, 374, 461, 488, 484, 482

Offset

1,1

Comments

Primes indexed by 3-almost primes = A124268. 3-almost primes indexed by primes = A124269. See also A106349 Primes indexed by semiprimes. See also A106350 Semiprimes indexed by primes.

Links

Giovanni Resta, Table of n, a(n) for n = 1..10000

Formula

a(n) = prime(3almostprime(n)) - 3almostprime(prime(n)) = A000040(A014612(n)) - A014612(A000040(n)).

Example

a(1) = prime(3almostprime(1)) - 3almostprime(prime(1)) = prime(8) - 3almostprime(2) = 19 - 12 = 7.
a(2) = prime(3almostprime(2)) - 3almostprime(prime(2)) = prime(12) - 3almostprime(3) = 37 - 18 = 19.
a(3) = prime(3almostprime(3)) - 3almostprime(prime(3)) = prime(18) - 3almostprime(5) = 61 - 27 = 34.

Prog

(PARI) lista(nn) = {p = primes(nn); pp = select(x->bigomega(x)==3, vector(nn, n, n)); for (n=1, nn, print1(p[pp[n]] - pp[p[n]], ", "); ); } \\ Michel Marcus, Oct 15 2014

Crossrefs

Cf. A000040 (primes), A014612 (3-almost primes).

Cf. A124268 (prime(3-almost prime(n)), A124269 (3-almost prime(primes(n)).

Cf. A106349 (prime(semiprime(n)), A106350 (semiprime(prime(n)), A122824 (Prime(semiprime(n)) - semiprime(prime(n)).

Sequence in context: A053591 A165333 A154878 * A298565 A068678 A069833

Adjacent sequences: A124267 A124268 A124269 * A124271 A124272 A124273

Keyword

easy,nonn

Author

Jonathan Vos Post, Oct 23 2006

Status

approved