A320633 Composite numbers whose prime indices are also composite.

49, 91, 133, 161, 169, 203, 247, 259, 299, 301, 329, 343, 361, 371, 377, 427, 437, 481, 497, 511, 529, 551, 553, 559, 611, 623, 637, 667, 679, 689, 703, 707, 721, 749, 791, 793, 817, 841, 851, 893, 917, 923, 931, 949, 959, 973, 989, 1007, 1027, 1043, 1057

Offset

1,1

Comments

A prime index of n is a number m such that prime(m) divides n.

Links

Table of n, a(n) for n=1..51.

Example

The sequence of terms begins:
   49 = prime(4)^2
   91 = prime(4)*prime(6)
  133 = prime(4)*prime(8)
  161 = prime(4)*prime(9)
  169 = prime(6)^2
  203 = prime(4)*prime(10)
  247 = prime(6)*prime(8)
  259 = prime(4)*prime(12)
  299 = prime(6)*prime(9)
  301 = prime(4)*prime(14)
  329 = prime(4)*prime(15)
  343 = prime(4)^3
  361 = prime(8)^2
  371 = prime(4)*prime(16)
  377 = prime(6)*prime(10)
  427 = prime(4)*prime(18)
  437 = prime(8)*prime(9)
  481 = prime(6)*prime(12)
  497 = prime(4)*prime(20)
  511 = prime(4)*prime(21)
  529 = prime(9)^2
  551 = prime(8)*prime(10)
  553 = prime(4)*prime(22)
  559 = prime(6)*prime(14)
  611 = prime(6)*prime(15)
  623 = prime(4)*prime(24)
  637 = prime(4)^2*prime(6)

Mathematica

Select[Range[2, 1000], And[OddQ[#], !PrimeQ[#], And@@Not/@PrimeQ/@PrimePi/@First/@FactorInteger[#]]&]

Crossrefs

Cf. A000040, A006450, A007821, A018252, A050370, A056239, A076610, A112798, A302242, A302478, A320533, A320628, A320629.

Sequence in context: A178705 A118886 A198773 * A108164 A020158 A084632

Adjacent sequences: A320630 A320631 A320632 * A320634 A320635 A320636

Keyword

nonn

Author

Gus Wiseman, Oct 18 2018

Status

approved