A090302 Begin with n and consider numbers obtained by successively subtracting 0, 1, 2, 3, ...; a(n) = largest prime that arises in the process, i.e., largest prime of the form n - T(r), where T(r) is the r-th triangular number; or 0 if no such number exists.

0, 2, 3, 3, 5, 5, 7, 7, 3, 7, 11, 11, 13, 13, 5, 13, 17, 17, 19, 19, 11, 19, 23, 23, 19, 23, 17, 13, 29, 29, 31, 31, 23, 31, 29, 0, 37, 37, 29, 37, 41, 41, 43, 43, 17, 43, 47, 47, 43, 47, 41, 37, 53, 53, 19, 53, 47, 43, 59, 59, 61, 61, 53, 61, 59, 11, 67, 67, 59, 67, 71

Offset: 1

Author

Amarnath Murthy, Nov 30 2003

Keywords

• nonn

Comments

a(p) = p if p is a prime.

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A076768 (positions of 0's).

Cf. A132399.

Formula

Largest prime of the form n - r(r+1)/2.

Extensions

More terms from Frank Ellermann, Dec 03 2003