A073896 a(1) = 1, a(n) = a(n-1) + k where k is smallest prime or composite number not used earlier according as a(n-1) is nonprime or prime.

1, 3, 7, 13, 21, 24, 29, 38, 45, 56, 69, 86, 105, 128, 157, 167, 179, 193, 208, 239, 255, 292, 333, 376, 423, 476, 535, 596, 663, 734, 807, 886, 969, 1058, 1155, 1256, 1359, 1466, 1575, 1688, 1815, 1946, 2083, 2101, 2240, 2389, 2409, 2560, 2717, 2880, 3047

Offset

1,2

Links

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

Example

a(2) = 1+2 = 3 which is prime hence a(3) = 3+4 = 7 which is also a prime,a(4)= 7+6 = 13 which is also prime hence a(5) = 13 + 8 = 21, composite hence a(6) =21+ 3= 24.

Crossrefs

Cf. A073895.

Sequence in context: A069194 A100531 A032409 * A299478 A355310 A299476

Adjacent sequences: A073893 A073894 A073895 * A073897 A073898 A073899

Keyword

nonn

Author

Amarnath Murthy, Aug 18 2002

Extensions

More terms from Sam Alexander, Mar 01 2005

Status

approved