For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (np) or the number of protons found in the nucleus of every atom of that element.
fɔːɹ ˈɔːɹdɪnˌɛɹi nˈuːklɪi kəmpˈoʊzd ʌv pɹˈoʊtɑːnz ænd nˈuːtɹɑːnz, ðɪs ɪz ˈiːkwəl tə ðə pɹˈoʊtɑːn nˈʌmbɚ ˌɛnpˈiː ɔːɹ ðə nˈʌmbɚɹ ʌv pɹˈoʊtɑːnz fˈaʊnd ɪnðə nˈuːklɪəs ʌv ˈɛvɹi ˈæɾəm ʌv ðæt ˈɛlɪmənt.