What is Almost prime?
A two-digit number <u>ab</u> is called '''almost prime''' if one obtains a two-digit prime number by changing at most one of its digits a and b. (For example, 18 is an almost prime number because 13 is a prime number). is called almost prime if one obtains a two-digit prime number by changing at most one of its digits and (For example, 18 is an almost prime number because 13 is a prime number).<ref>{{Cite book|title=Handbook of Number Theory I|url=https://archive.org/details/handbookofnumber0000jsnd|last1=Sándor|first1=József|last2=Dragoslav|first2=Mitrinović S.|last3=Crstici|first3=Borislav|publisher=[[Springer Science+Business Media|Springer]]|year=2006|isbn=978-1-4020-4215-7|page=[https://archive.org/details/handbookofnumber0000jsnd/page/316 316]|doi=10.1007/1-4020-3658-2}}</ref><ref>{{Cite journal|last=Rényi|first=Alfréd A.|author-link=Alfréd Rényi|year=1948|title=On the representation of an even number as the sum of a single prime and single almost-prime number|url=http://www.mathnet.ru/php/archive.phtml?wshow=paper&jrnid=im&paperid=3018&option_lang=eng|journal=Izvestiya Rossiiskoi Akademii Nauk. Seriya Matematicheskaya|language=ru|volume=12|issue=1|pages=57–78}}</ref><ref>{{Cite journal|last=Heath-Brown|first=D. R.|author-link=Roger Heath-Brown|date=May 1978|title=Almost-primes in arithmetic progressions and short intervals|journal=Mathematical Proceedings of the Cambridge Philosophical Society|volume=83|issue=3|pages=357–375|bibcode=1978MPCPS..83..357H|doi=10.1017/S0305004100054657|s2cid=122691474 }}</ref> == References == {{reflist}} [[Category:Prime numbers]] [[Category:Integer sequences]]