A318896 Numbers k such that k and k+1 are the product of exactly four distinct primes.

7314, 8294, 8645, 11570, 13629, 13845, 15105, 15554, 16554, 17390, 17654, 18290, 19005, 20405, 20769, 21489, 22010, 22154, 23001, 23114, 23529, 24530, 24765, 24870, 24969, 25346, 26690, 26894, 26961, 27434, 27965, 28105, 29145, 29210, 29414, 29469, 29666, 30414

Offset: 1

Author

Seiichi Manyama, Sep 05 2018

Keywords

• nonn

Comments

This sequence is different from A140078. For example, A140078(4) = 9009 = 3^2 * 7 * 11 * 13 is not a term.

Examples

			n | a(n)                    | a(n)+1
--+-------------------------+-------------------------
1 | 7314 = 2 *  3 * 23 * 53 | 7315 = 5 * 7 * 11 *  19
2 | 8294 = 2 * 11 * 13 * 29 | 8295 = 3 * 5 *  7 *  79
3 | 8645 = 5 *  7 * 13 * 19 | 8646 = 2 * 3 * 11 * 131
		

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A140078.

Cf. A046386, A052215, A215217, A263990, A318964.

Programs

PARI

is(n) = omega(n)==4 && omega(n+1)==4 && bigomega(n)==4 && bigomega(n+1)==4 \\ Felix Fröhlich, Sep 05 2018

PARI

is(n) = factor(n)[, 2]~ == [1, 1, 1, 1] && factor(n+1)[, 2]~ == [1, 1, 1, 1] \\ David A. Corneth, Sep 06 2018