A076207 Triangular numbers whose sum of primes from smallest to largest prime factor is triangular and whose sum of composites from smallest to largest prime factor is triangular.

3, 21, 105, 325, 7875, 9568125

Offset

1,1

Comments

No more terms < 2.77*10^12. - David Wasserman, Jul 20 2005

a(7) > 2*10^15. - Donovan Johnson, Feb 03 2013

Links

Table of n, a(n) for n=1..6.

Example

325 = 5^2*13, sum of primes between: 5+7+11+13 = 36, triangular; sum of composites between: 6+8+9+10+12 = 45, triangular.

Crossrefs

Cf. A000217, A074036, A074037.

Sequence in context: A241795 A289399 A306093 * A134057 A128281 A034268

Adjacent sequences: A076204 A076205 A076206 * A076208 A076209 A076210

Keyword

more,nonn

Author

Jason Earls, Nov 02 2002

Extensions

Offset corrected by Donovan Johnson, Feb 03 2013

Status

approved