A115404 Numbers n such that n^4+1 is a 4-almost prime (product of four primes).

43, 59, 77, 79, 83, 85, 95, 111, 127, 137, 147, 155, 178, 179, 185, 202, 221, 223, 227, 229, 233, 239, 241, 247, 249, 253, 261, 263, 270, 271, 273, 285, 287, 297, 314, 331, 338, 341, 342, 357, 359, 387, 389, 393, 395, 401, 408, 413, 421, 427, 433, 435, 437

Offset

1,1

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

n^4+1=p*q*r*s where p, q, r, s are primes (not necessarily distinct).

Example

43 is OK because 43^4+1=3418802=2*17*193*521 (product of four primes).

Mathematica

Select[Range[500], Sum[FactorInteger[ #^4 + 1][[i]][[2]], {i, 1, Length[FactorInteger[ #^4 + 1]]}] == 4 &] (* Stefan Steinerberger, Mar 09 2006 *)

Prog

(PARI) is(n)=bigomega(n^4+1)==4 \\ Charles R Greathouse IV, Oct 11 2013

Crossrefs

Cf. A014613 = 4-almost primes.

Sequence in context: A127880 A078132 A201613 * A033223 A215538 A378851

Adjacent sequences: A115401 A115402 A115403 * A115405 A115406 A115407

Keyword

nonn

Author

Zak Seidov, Mar 08 2006

Status

approved