Numbers k such that Sum_{j=1..k} sigma(j) is a triangular number, where sigma(j) = sum of divisors of j (A000203).

A226648

Numbers k such that Sum_{j=1..k} sigma(j) is a triangular number, where sigma(j) = sum of divisors of j (A000203).

Terms

    a(0) =1a(1) =4a(2) =5a(3) =50a(4) =64a(5) =906a(6) =966a(7) =5805a(8) =40514a(9) =133667a(10) =262277a(11) =1416109a(12) =42142704a(13) =189758142a(14) =350476553a(15) =957982453a(16) =1420733777a(17) =1421477786a(18) =2557347701a(19) =28609375750a(20) =95023678204a(21) =100094778026a(22) =119964793932

External references