A101757 Indices of semiprimes in A000073.

5, 12, 18, 42, 44, 50, 58, 67, 74, 83, 90, 95, 126, 142, 194, 210, 211, 275, 367, 382, 479, 655, 734, 818, 839, 926, 939, 1047

Offset

1,1

Comments

a(29) >= 1091. A000073(1091) is a 288-digit composite number with unknown factorization. Other possible terms are 1390, 1630, 2034, 2131, 2339, ... - Tyler Busby, Feb 09 2023

Links

Table of n, a(n) for n=1..28.

Eric Weisstein's World of Mathematics, Semiprime

Formula

A000073(a(n)) = A101758(n).

Mathematica

Flatten[Position[LinearRecurrence[{1, 1, 1}, {1, 1, 2}, 100], _?(PrimeOmega[ #]==2&)]]+1 (* This generates the first 12 terms of the sequence.  To generate more, increase 100 to a higher number, but it will take increasingly long to run. *) (* Harvey P. Dale, May 31 2013 *)

Crossrefs

Cf. A000073, A001358, A101758.

Equivalent sequence for primes: A303263.

Sequence in context: A314290 A246300 A294143 * A174518 A109403 A093084

Adjacent sequences: A101754 A101755 A101756 * A101758 A101759 A101760

Keyword

nonn,more,less

Author

Jonathan Vos Post and Ray Chandler, Dec 26 2004

Extensions

More terms from David Wasserman, Apr 03 2008

Status

approved