Term

Emirp

Primes whose digit reversal is a different prime (13, 17, 31, 37, 71, 73, 79, 97, 107, 113, …).

1,646 numbers tagged.

An emirp — "prime" spelled backwards — is a prime that becomes a different prime when its digits are reversed. 13 ↔ 31, 17 ↔ 71, 37 ↔ 73, 79 ↔ 97. Palindromic primes like 101 are excluded: the reversal must differ.

Emirp pairs come two by two, each member pointing at the other. The largest known emirps have thousands of digits. Like most digit-based properties, being an emirp depends on the base — a base-10 emirp need not be one in binary.

13 17 31 37 71 73 79 97 107 113 149 157 167 179 199 311 337 347 359 389 701 709 733 739 743 751 761 769 907 937 941 953 967 971 983 991 1,009 1,021 1,031 1,033 1,061 1,069 1,091 1,097 1,103 1,109 1,151 1,153 1,181 1,193 1,201 1,213 1,217 1,223 1,229 1,231 1,237 1,249 1,259 1,279 1,283 1,301 1,321 1,381 1,399 1,409 1,429 1,439 1,453 1,471 1,487 1,499 1,511 1,523 1,559 1,583 1,597 1,601 1,619 1,657 1,669 1,723 1,733 1,741 1,753 1,789 1,811 1,831 1,847 1,867 1,879 1,901 1,913 1,933 1,949 1,979 3,011 3,019 3,023 3,049 3,067 3,083 3,089 3,109 3,121 3,163 3,169 3,191 3,203 3,221 3,251 3,257 3,271 3,299 3,301 3,319 3,343 3,347 3,359 3,371 3,373 3,389 3,391 3,407 3,433 3,463 3,467 3,469 3,511 3,527 3,541 3,571 3,583 3,613 3,643 3,697 3,719 3,733 3,767 3,803 3,821 3,851 3,853 3,889 3,911 3,917 3,929 7,027 7,043 7,057 7,121 7,177 7,187 7,193 7,207 7,219 7,229 7,253 7,297 7,321 7,349 7,433 7,457 7,459 7,481 7,507 7,523 7,529 7,547 7,561 7,577 7,589 7,603 7,643 7,649 7,673 7,681 7,687 7,699 7,717 7,757 7,817 7,841 7,867 7,879 7,901 7,927 7,949 7,951 7,963 9,001 9,011 9,013 9,029 9,041 9,103 9,127 9,133 9,161 9,173

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