Every Day Counts
Centred Square Prime Days
 
Age: 20,194 days
Date of birth
Your 36th Centred Square Prime Day is on
Tuesday
when you will be
20,201 days old

A centred square prime is a centred square number that is prime.

Unlike regular square numbers, which are never prime, quite a few of the centred square numbers are prime.

Centred square numbers are of the form n2 + (n - 1)2

In elementary number theory, a centred square number is a centred figurate number that gives the number of dots in a square with a dot in the centre and all other dots surrounding the centre dot in successive square layers. That is, each centred square number equals the number of dots within a given city block distance of the centre dot on a regular square lattice. While centred square numbers, like figurate numbers in general, have few if any direct practical applications, they are sometimes studied in recreational mathematics for their elegant geometric and arithmetic properties.

The figures for the first four centred square numbers are shown below:

Remind me, please


Next Prime Events
Day Age
Event
Days Ahead
Year Age
08 Jul 2025
20,201
7
55
08 Jul 2025
20,201
7
55
11 Dec 2025
20,357
163
55
13 Dec 2025
20,359
165
55
16 Aug 2029
21,701
1,507
59
01 Sep 2031
22,447
2,253
61
01 Sep 2048
28,657
8,463
78
17 Aug 2052
30,103
9,909
82
21 Jan 2072
37,199
17,005
101
28 Dec 2077
39,367
19,173
107
29 Nov 2089
43,721
23,527
119
29 Apr 2103
48,619
28,425
133
23 Aug 2149
65,537
45,343
179
06 Oct 2244
100,279
80,085
274
25 Apr 2268
108,881
88,687
298
26 Jan 2329
131,071
110,877
358
20 May 7787
2,124,679
2,104,485
5817
Ordinal
Day Age
Date
Age
1st
5
23 Mar 1970
0
2nd
13
31 Mar 1970
0
3rd
41
28 Apr 1970
0
4th
61
18 May 1970
0
5th
113
09 Jul 1970
0
6th
181
15 Sep 1970
0
7th
313
25 Jan 1971
0
8th
421
13 May 1971
1
9th
613
21 Nov 1971
1
10th
761
17 Apr 1972
2
11th
1,013
25 Dec 1972
2
12th
1,201
01 Jul 1973
3
13th
1,301
09 Oct 1973
3
14th
1,741
23 Dec 1974
4
15th
1,861
22 Apr 1975
5
16th
2,113
30 Dec 1975
5
17th
2,381
23 Sep 1976
6
18th
2,521
10 Feb 1977
6
19th
3,121
03 Oct 1978
8
20th
3,613
07 Feb 1980
9
21st
4,513
26 Jul 1982
12
22nd
5,101
05 Mar 1984
13
23rd
7,321
03 Apr 1990
20
24th
8,581
14 Sep 1993
23
25th
9,661
29 Aug 1996
26
26th
9,941
05 Jun 1997
27
27th
10,513
29 Dec 1998
28
28th
12,641
26 Oct 2004
34
29th
13,613
25 Jun 2007
37
30th
14,281
23 Apr 2009
39
31st
14,621
29 Mar 2010
40
32nd
15,313
19 Feb 2012
41
33rd
16,381
22 Jan 2015
44
34th
19,013
07 Apr 2022
52
35th
19,801
03 Jun 2024
54
36th
20,201
08 Jul 2025
55
1
37th
21,013
28 Sep 2027
57
38th
21,841
03 Jan 2030
59
39th
23,981
13 Nov 2035
65
40th
24,421
26 Jan 2037
66
41st
26,681
05 Apr 2043
73