A247606 Number of non-semiprimes among "preprimes" of the n-th kind (defined in comment in A247395).

1, 7, 15, 36, 31, 62, 59, 111, 161, 113, 224, 175, 155, 258, 370, 358, 240, 436, 346, 297, 557, 504, 691, 806, 477, 367, 554, 489, 938, 1743, 786, 959, 725, 1526, 669, 1215, 1207, 1022, 1359, 1286, 958, 1947, 773, 1206, 1328, 3078, 2740, 1165, 915, 1459, 1787

Offset: 1

Author

Vladimir Shevelev, Sep 22 2014

Keywords

• nonn

Comments

One can prove that non-semiprimes we can find among preprimes of the n-th kind only with the smallest prime divisor 2,3,...,prime(n), where n=1 corresponds to A156759, n=2 corresponds to A247393, n=3 corresponds to A247394, etc. For example, for n=1, only among even numbers of A156759; for n=2 - only among even numbers and numbers with the smallest prime divisor 3 of A247393, etc. Thus, for every n>=1, among preprimes of the n-th kind almost all numbers are semiprimes.

Links

• Vladimir Shevelev, A classification of the positive integers over primes

Crossrefs

Cf. A156759, A247393, A247394, A247395, A247396, A247509, A247510, A247511.

Extensions

More terms from Peter J. C. Moses, Sep 22 2014