cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

User: Parthasarathy Nambi

Parthasarathy Nambi's wiki page.

Parthasarathy Nambi has authored 789 sequences. Here are the ten most recent ones:

A181473 Digital root of EKG sequence.

Original entry on oeis.org

1, 2, 4, 6, 3, 9, 3, 8, 1, 5, 6, 9, 5, 7, 3, 6, 7, 2, 4, 2, 6, 9, 3, 7, 8, 1, 8, 4, 3, 9, 5, 7, 8, 6, 6, 2, 1, 3, 9, 4, 8, 1, 5, 6, 3, 5, 7, 9, 2, 4, 9, 6, 1, 2, 7, 4, 2, 6, 3, 8, 4, 3, 9, 1, 5, 2, 1, 3, 3, 6, 4, 8, 1, 5, 6, 9, 3, 5, 7, 5, 7, 3, 9, 4, 5, 1, 2, 4, 2, 6, 6, 8, 1, 5, 3, 9, 6, 9, 7, 8, 6, 6, 2, 4, 8
Offset: 1

Views

Author

Parthasarathy Nambi, Oct 22 2010

Keywords

Examples

			Digital root of the number 11 is 2

Crossrefs

Cf. A010888, A064413.

A181548 Digital sum of EKG sequence.

Original entry on oeis.org

1, 2, 4, 6, 3, 9, 3, 8, 1, 5, 6, 9, 5, 7, 3, 6, 7, 2, 4, 2, 6, 9, 3, 7, 8, 10, 8, 4, 12, 9, 5, 7, 8, 6, 6, 11, 10, 12, 9, 4, 8, 10, 5, 15, 12, 5, 7, 9, 11, 13, 9, 6, 10, 11, 7, 13, 11, 15, 12, 8, 4, 12, 9, 10, 14, 11, 10, 3, 12, 15, 13, 8, 10, 5, 6, 9, 12, 14, 16, 14, 7, 12, 9, 13, 14, 1, 11, 13, 11, 6, 15, 17, 10, 5, 3, 18, 6, 9, 7, 8
Offset: 1

Views

Author

Parthasarathy Nambi, Oct 30 2010

Keywords

Examples

			10 is the digital sum of 82 which is a term in the EKG sequence.

Links

Crossrefs

Cf. A007953, A064413.

Extensions

Duplicated terms a(58)-a(60) removed and more terms from Georg Fischer, Dec 23 2024

A180022 Primes that can be obtained from other primes by interchanging the first and last digits. The source prime and the resulting prime are written consecutively.

Original entry on oeis.org

11, 11, 13, 31, 17, 71, 31, 13, 37, 73, 71, 17, 73, 37, 79, 97, 97, 79, 101, 101, 107, 701, 113, 311, 131, 131, 149, 941, 151, 151, 157, 751, 167, 761, 179, 971, 181, 181, 191, 191, 199, 991, 311, 113, 313, 313, 337, 733, 347, 743, 353, 353, 359, 953, 373, 373
Offset: 1

Views

Author

Parthasarathy Nambi, Aug 06 2010

Keywords

Comments

This sequence is different from A007500 and A069706. [From Parthasarathy Nambi, Aug 07 2010]

Examples

			389 is a prime and the prime 983 is obtained by interchanging the first and last digits.

Crossrefs

Cf. A179826, A180006
Cf. A007500,A069706. [From Parthasarathy Nambi, Aug 07 2010]

A180108 Integers where the primes are split into two consecutive numbers.

Original entry on oeis.org

0, 1, 2, 1, 2, 4, 2, 3, 6, 3, 4, 8, 9, 10, 5, 6, 12, 6, 7, 14, 15, 16, 8, 9, 18, 9, 10, 20, 21, 22, 11, 12, 24, 25, 26, 27, 28, 14, 15, 30, 15, 16, 32, 33, 34, 35, 36, 18, 19, 38, 39, 40, 20, 21, 42, 21, 22, 44, 45, 46, 23, 24, 48, 49, 50, 51, 52, 26, 27, 54, 55, 56, 57, 58, 29, 30
Offset: 0

Views

Author

Parthasarathy Nambi, Aug 10 2010

Keywords

Comments

The even prime 2 is not split.

Examples

			The prime 29 is split into 14 and 15.

Crossrefs

Cf. A000040, A002808.

Programs

  • Mathematica
    f[n_] := If[ !PrimeQ@ n || n == 2, n, {(n - 1)/2, (n + 1)/2}]; Array[ f, 60, 0] // Flatten (* Robert G. Wilson v, Aug 15 2010 *)

Extensions

More terms from Robert G. Wilson v, Aug 15 2010

A180006 Composite numbers that can be obtained from primes by interchanging the first and last digits.

Original entry on oeis.org

91, 32, 92, 14, 34, 74, 35, 95, 16, 76, 38, 98, 301, 901, 721, 731, 931, 361, 371, 391, 791, 112, 322, 722, 922, 332, 932, 142, 152, 752, 362, 962, 172, 772, 182, 382, 392, 703, 713, 133, 943, 763, 973, 793, 104, 904, 914, 124, 134, 334, 934, 344, 944, 754
Offset: 1

Views

Author

Parthasarathy Nambi, Aug 06 2010

Keywords

Comments

The primes must contain at least two digits.

Examples

			The composite number 752 is obtained from the prime 257 by interchanging the first and last digits.

Links

Crossrefs

The corresponding primes are A076056. Cf. A002808, A179826.

Programs

  • Mathematica
    Select[With[{idn=IntegerDigits[#]},FromDigits[Join[{idn[[-1]]},Most[Rest[idn]],{idn[[1]]}]]]&/@Prime[Range[5,1500]],CompositeQ] (* Harvey P. Dale, Jan 26 2025 *)

Extensions

More terms from Vincenzo Librandi, Aug 06 2010

A180156 Sequence from adding the twin primes and dividing by the digit sum of twin primes.

Original entry on oeis.org

1, 1, 4, 2, 4, 7, 6, 8, 34, 12, 12, 14, 13, 16, 11, 19, 23, 20, 24, 52, 23, 40, 48, 39, 58, 35, 40, 41, 54, 40, 60, 69, 46, 41, 49, 136, 172, 100, 118, 91, 128, 117, 71, 78, 217, 126, 95, 121, 99, 71, 107, 120, 79, 71, 144, 75, 104, 78, 129, 100, 74, 169, 174, 116, 352, 203, 238
Offset: 1

Views

Author

Parthasarathy Nambi, Aug 14 2010

Keywords

Comments

If necessary the result is rounded to the nearest integer.
This sequence uses round(x) = floor(1/2 + x). - Jason Yuen, Sep 01 2025

Examples

			a(7) = round((59 + 61) / (5+9+6+1)) = round(120/21) = round(5.714...) = 6.
a(10) = round((107 + 109) / (1+0+7+1+0+9)) = round(216/18) = 12.

Links

Crossrefs

Cf. A001359.

Programs

  • Mathematica
    Floor[1/2+Total[#]/Total[Flatten[IntegerDigits/@#]]]&/@ Select[Partition[Prime[Range[500]],2,1], Last[#]-First[#]==2&]  (* Harvey P. Dale, Mar 23 2011 *)
f[n_] := Floor[1/2 + 2 (n + 1)/(Plus @@ IntegerDigits[n] + Plus @@ IntegerDigits[n + 2])]; f@# & /@ Select[ Prime@ Range@ 1000, PrimeQ[# + 2] &] (* Robert G. Wilson v, Aug 16 2011 *)

Extensions

More terms from Harvey P. Dale, Mar 23 2011

A179826 Primes that can be obtained from composite numbers by interchanging the first and last digits.

Original entry on oeis.org

41, 61, 2, 3, 23, 43, 53, 83, 5, 7, 47, 67, 19, 29, 59, 89, 401, 601, 11, 211, 811, 911, 421, 521, 821, 31, 331, 431, 631, 41, 241, 541, 641, 251, 61, 461, 661, 71, 271, 571, 281, 881, 491, 691, 2, 3, 103, 503, 13, 613, 23, 223, 523, 823, 233, 433, 43, 443, 643, 53
Offset: 1

Views

Author

Parthasarathy Nambi, Jul 29 2010

Keywords

Comments

The composite number must contain at least two digits.
Primes may be repeated; the reverted A002808(j) are investigated along increasing j and their trailing zeros become leading zeros and are dropped. [R. J. Mathar, Jul 30 2010]

Examples

			41 is a prime from the composite number 14 by interchanging the first and last digit. 47 is a prime from the composite number 74 by interchanging the first and last digit.

Programs

  • Mathematica
    nonpr=Complement[Range[10,1000],Prime[Range[PrimePi[1000]]]];
swtch[n_]:=Module[{idn=IntegerDigits[n],f,l,m},f=First[idn];l=Last[idn];m=Most[Rest[idn]];FromDigits[Join[{l},m,{f}]]]
Select[swtch[#]&/@nonpr,PrimeQ] (* Harvey P. Dale, Dec 14 2010 *)

Extensions

Minor edits by N. J. A. Sloane, Jul 29 2010
More terms from R. J. Mathar, Jul 30 2010

A157662 Composite numbers such that the last digit is equal to the sum of all the previous digits.

Original entry on oeis.org

112, 123, 134, 145, 156, 178, 189, 202, 213, 224, 235, 246, 268, 279, 303, 314, 325, 336, 358, 369, 404, 415, 426, 437, 448, 459, 505, 516, 527, 538, 549, 606, 628, 639, 707, 718, 729, 808, 819, 909, 1001, 1012, 1023
Offset: 1

Views

Author

Parthasarathy Nambi, Mar 04 2009

Keywords

Comments

Numbers such as 11, 22, 33 are ignored.

Examples

			1023 is a composite number where the last digit is the sum of all the previous digits.

Crossrefs

A002808, A157496, A157529

A158921 Positions of hexanacci numbers in the EKG sequence.

Original entry on oeis.org

1, 2, 3, 8, 17, 31, 51, 112, 234, 464, 931, 1855, 3687, 4877
Offset: 1

Views

Author

Parthasarathy Nambi, Mar 30 2009

Keywords

Examples

			The hexanacci number 7617 is located at position 4877 in the EKG sequence.

Crossrefs

A001592, A064413, A140897, A144080

A162658 Primes such that the sum of its smallest and largest decimal digits is an odd prime.

Original entry on oeis.org

23, 29, 41, 47, 61, 67, 83, 103, 107, 163, 211, 223, 229, 233, 241, 269, 293, 307, 383, 421, 431, 433, 443, 449, 457, 461, 467, 479, 491, 499, 503, 509, 523, 547, 587, 607, 613, 631, 641, 661, 677, 701, 829, 853, 857, 863, 883, 929, 947
Offset: 1

Views

Author

Parthasarathy Nambi, Jul 09 2009

Keywords

Examples

			947 is a prime in which the sum of the smallest digit (4) and the largest digit (9) is an odd prime (13).

Crossrefs

A046704, A070027, A086244, A088136, A091939, A109981

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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