A268583 Happycab numbers: the smallest happy number that is the sum of two cubes of happy numbers in n different ways.

7859, 681179092750, 4466203788801326865111

Offset: 1

Author

Corinna Regina Böger, Feb 07 2016

Keywords

• nonn
• hard
• more
• bref

Comments

a(n)>3.6*10^24 for n >=4. This lower bound was established by exhaustive crowd computing.

Upper bounds:

a(4)<= 3915335521240189321820073984

=467175960^3+1562319144^3

=569783808^3+1550898288^3

=1085420968^3+1381483928^3

=1157553216^3+1332193392^3

a(5)<=

1508202165690304620654479410485250200981504

=12156471201588^3+114634141265868^3

=33798481396036^3+113692639229372^3

=64341822928208^3+107486686558048^3

=69397851840576^3+105492106344912^3

=72561474196232^3+104039736026296^3

Examples

			a(1) = 7859 = 10^3+19^3;
a(2) = 681179092750 = 4365^3+8425^3 = 5275^3+8115^3;
a(3) = 4466203788801326865111 = 6193863^3+16170804^3 = 8456292^3+15688647^3 = 9457695^3+15354846^3.
		

Crossrefs

Cf. A011541, A007770.