The place is the supply code about this default connection depend？

static const int MAX_OUTBOUND_FULL_RELAY_CONNECTIONS = 8;
/** Most variety of addnode outgoing nodes */
static const int MAX_ADDNODE_CONNECTIONS = 8;
/** Most variety of block-relay-only outgoing connections */
static const int MAX_BLOCK_RELAY_ONLY_CONNECTIONS = 2;

/** The utmost variety of peer connections to keep up. */
static const unsigned int DEFAULT_MAX_PEER_CONNECTIONS = 125;

https://github.com/bitcoin/bitcoin/blob/grasp/src/internet.h#L66
https://github.com/bitcoin/bitcoin/blob/grasp/src/internet.h#L76

There is usually a most of 16 outgoing full relay connections, together with 8 automated and eight guide.
Moreover, there are two block relay connections.
Subsequently, a node that begins up for the primary time has 10 by default after a short time.

Can i exploit some command to set this quantity when beginning bitcoind？

You should use -maxconnections for sustaining at most N connections to friends nonetheless this consists of outbound and inbound. It’s 125 by default.

Some modifications to the supply code shall be required if you wish to make outbound connections depend configurable: Improve most variety of outgoing connections for full node

You may also enhance connection depend by incoming connections. This doc consists of directions and settings to setup node and pay attention for incoming connections utilizing i2p: https://github.com/bitcoin/bitcoin/blob/grasp/doc/i2p.md