A101398 -id:A101398 - cp's OEIS frontend

A230006 Numbers k such that sigma(k) + phi(k) = reversal(k) + 1.

1, 37, 225, 397, 11112722, 1309286244182

Offset: 1

Farideh Firoozbakht, Dec 02 2013

If p = 4*10^m-3 is prime then p is in the sequence.

a(7) > 10^13. - Giovanni Resta, Feb 08 2014

			sigma(37)+phi(37) = 38+36 = 73+1 = reversal(37)+1.

Cf. A000010, A000203, A004086, A101398, A230004, A230005.

r[n_] := FromDigits[Reverse[IntegerDigits[n]]]; Do[If[DivisorSigma[1, n] + EulerPhi[n] == r[n]+1, Print[n]], {n, 1000000000}]

a(6) from Giovanni Resta, Feb 06 2014

A101849 Indices of primes in sequence defined by A(0) = 37, A(n) = 10*A(n-1) + 27 for n > 0.

Original entry on oeis.org

0, 1, 13, 19, 29, 43, 65, 259, 871, 8845, 26743, 57505, 98471, 106891

Offset: 1

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004

Numbers n such that (360*10^n - 27)/9 is prime.
Numbers n such that digit 3 followed by n >= 0 occurrences of digit 9 followed by digit 7 is prime.
Numbers corresponding to terms <= 871 are certified primes.
a(14) > 10^5. - Robert Price, Mar 17 2015.
a(15) > 2*10^5. - Robert Price, Oct 02 2015

			397 is prime, hence 1 is a term.

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Makoto Kamada, Prime numbers of the form 399...997.
Index entries for primes involving repunits.

Cf. A000533, A002275, A101155, A169830, A101398.

Select[Range[0, 1000], PrimeQ[(360*10^# - 27)/9] &] (* Robert Price, Mar 17 2015 *)

a=37;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+27)

for(n=0,1500,if(isprime((360*10^n-27)/9),print1(n,",")))

a(n) = A101398(n) - 1.

8845 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(11)-a(13) derived from A101398 by Robert Price, Mar 17 2015
a(14) from Robert Price, Oct 02 2015

cp's OEIS Frontend

A230006 Numbers k such that sigma(k) + phi(k) = reversal(k) + 1.

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